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TITLE: CATALYSTS FOR THE CONVERSION OF SYNTHESIS GAS TO
ALCOHOLS
FIELD OF THE APPLICATION
[0001] The present application generally relates to the field of catalysts for
the chemical conversion of synthesis gas to alcohols.
BACKGROUND OF THE APPLICATION
[0002] The synthesis of higher alcohols from synthesis gas by direct
catalysis was recognized in 1923 by Frans Fischer and Hans Tropsch. They
reported that a mixture of alcohols, aldehydes, ketones, fatty acids, and
esters
were formed when the reaction between CO and H2 was performed at pressures
ranging from 10 to 14 MPa and at temperatures of 400 to 500 C in the presence
of an alkalized iron oxide catalyst. They named the mixture as synthol and the
process as the synthol process.' In 1930, Frolich and Cryder reported the
formation of alcohols higher than methanol by passing syngas over a Zn:Mn:Cr,
1:1.1:1.03 catalyst. They reported that methanol forms from a formaldehyde
intermediate and that the higher alcohols form from the methanol through a
stepwise condensation reaction.2 In the 1940s, Du Pont developed an alkalized
Mn-Cr catalyst to synthesize methanol and higher alcohols from syngas for
commercial purposes.3 In the late 1940s, Farbenindustrie et al. introduced the
Synol process for the manufacture of alcohols from syngas. This process uses
low pressures around 2 MPa with higher productivity of alcohols by modifying
the
Fischer-Tropsch alkalized iron catalyst.4 Natta et al. reviewed the synthesis
of
higher alcohols from CO and H2, in 1957 and reported that the synthesis of
higher alcohols was always related to the presence of strongly basic
substances.5
[0003] Higher alcohols synthesis from CO hydrogenation is of interest as
the alcohol mixture is an effective octane number enhancer for motor fuels.6,7
The catalytic systems used for the higher alcohols synthesis reaction from
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synthesis gas are divided into two groups, based on the product distribution.8
Alkali-doped high temperature ZnCrO-based and low temperature Cu-based
catalytic systems produce mainly methanol and higher branched alcohols.9 The
second group developed from Fe, Ni, or Co modified low temperature and low
pressure methanol synthesis catalysts and alkali-modified MoS2-based catalysts
yields a series of linear primary alcohols and gaseous hydrocarbons with
Anderson-Schulz-Flory (ASF) carbon number distributions. 10
[0004] Alkali-modified MoS2-based catalysts are commercially attractive
among different higher alcohols synthesis catalysts, due to their excellent
sulfur
resistance and high activity for water-gas shift (WGS) reactions." The
promotion
of Pt group metals, especially Rh in Mo-based catalysts, improved activity
toward
the formation of higher alcohols.12 The Mo promotion over the Rh/A1203
catalyst
increased its activity favoring the formation of oxygenates.13 Li et al.14
explained
that a strong interaction occurred between the rhodium modifiers with the
supported K-Mo-O species in the oxidic Rh modified Mo-K/A1203 samples and
concluded that the coexistence of cationic and metallic Rh stabilized by this
interaction may be responsible for the increased selectivity toward higher
alcohols (C2+OH). Foley et al.15 suggested that the interaction between Rh and
Mo leads to the formation of electron-poor sites that are responsible for the
formation of alcohols. Shen et al.16 investigated the promotion effect of Mo
in Rh-
Mo/SiO2 catalysts in an oxided state and suggested that Mo promotion either
leads to the oxidation of Rh and consequent stabilization Rh'+ ions or the
coverage of Rh sites by Mo oxides, depending on the interaction between Rh
and Mo. Depending on the status of the rhodium species, properties of alkali
promoters, nature of the support, and reaction conditions, the rhodium species
are capable of catalyzing dissociation, insertion, and CO hydrogenation. 17
[0005] The addition of 3d transition metals, such as Co and Ni to M0S2,
has a strong promotion effect on the CO hydrogenation reaction.18 ' 19 The
promotion of Co (or Ni) on M0S2 leads to the formation of three different
phases:
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M0S2, Co9S8 (Ni3S2), and a mixed Co (Ni)-Mo-S phase.20 The formation of the Co
(Ni)-Mo-S phase is related to the electron donation from Co (Ni) to Mo
decreasing the Mo-S bond strength to an optimum range, thus significantly
increasing the activity of the catalyst. 21 The Co-promoted alkali-modified
molybdenum sulfide catalysts showed better activity and selectivity of higher
alcohols compared to that of Ni.22 The Ni promotion on alkali-modified M9S2
catalysts favors the formation of hydrocarbon as Ni is a methanation
component.23 Fujumoto et al.24 found that equal amounts of hydrocarbons and
alcohols resulted from the CO hydrogenation reaction over the K/Co/Mo/A1203
and K/Co/Mo/Si02 catalysts. Li et al.10 introduced Co as a promoter to
activated
carbon-supported K-M0S2 catalysts and found that Co exists mainly in the form
of the Co-Mo-S phase at low Co loading and partly in a Co9S8-like structure at
high Co content. The addition of Co to alkali-modified M0S2 catalysts enhanced
the C1 --+ C2 homologation step that leads to the formation of ethanol as the
dominant product. 25 Wong et al.26 investigated the incorporation of Rh into
reduced K/Co/Mo/A1203 catalysts and found that the activity and selectivity of
alcohols improved significantly due to the interaction of cationic Rh species
with
the Mo species.
[0006] Catalyst support plays an important role for reactions involving
hydrogen as a reactant or product. Supports such as activated carbon,27
clay,28
A1203, 29 Si02, 30 Ce02, 31 Zr02, 32 and combinations of different metal
oxides 33
have been studied in detail as supports to different catalyst systems for
higher
alcohols synthesis reactions from synthesis gas. Acidic metal oxide supports,
such as A1203 and Zr02, favor the formation of hydrocarbons by suppressing the
reaction rate of alcohols and their surface acidity causes deactivation by
coke
formation.34 35 Concha et al.36 compared the effects of different support s
(Si02,
AI203, activated carbon, and CeO2) on reduced and sulfided molybdenum
catalysts and found that hydrocarbon selectivity on activated carbon-supported
37
catalysts was much less than that of others. Murchison et al. found that MoS2
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supported on activated carbon showed alcohol selectivity about six times
higher
than that of the alumina-supported catalyst. Activated carbon has many
advantages as a catalyst support because of its large surface area, limited
interaction between the support, and the active material due to the inertness
of
the graphitic surface, resistance to acidic or basic media, and stability at
high
temperatures and pressures.38 However, activated carbon supported catalysts
have a microporous structure (pore size < 2 nm) that causes pore plugging due
to the formation of coke and deactivation of the catalyst, which results in
transport limitation in the reaction.39 Also, activated carbons have 10-15%
ash
content, depending on the nature of the precursor used.40
[0007] Carbon, in the form of multiwalled carbon nanotubes (MWCNTs), is
an alternative heterogeneous catalyst support having characteristics similar
to
activated carbon, such as an inert graphite nature and high temperature
stability.41,42,43
SUMMARY OF THE APPLICATION
[0008] In the present application, it has been demonstrated that the
addition of Co and Rh metal promoters to alkali-promoted MOS2 catalysts
supported on, for example MWCNTs, display improved catalytic performance
towards higher alcohols formation from synthesis gas. The alkali-promoted
trimetallic Co-Rh-Mo catalyst system is representative of a class of
trimetallic
catalysts that are advantageous as they have increased activity and
selectivity
for the formation of higher alcohols, especially ethanol.
[0009] Accordingly, the present application includes a catalyst comprising
the Formula (I):
A-M'-M2-M3 (I)
wherein A is an alkali metal;
M1 is selected from Co, Ni and Fe;
M2 is selected from Rh, Ru and Pd; and
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M3 is selected from Mo;
wherein the catalyst is supported on a carbon-based material.
[0010] In an embodiment the catalyst comprises the Formula A-Co-Rh-Mo,
wherein A is an alkali metal, for example K, and the catalyst is supported on
a
carbon-based support selected from activated carbon and multi-walled carbon
nano-tubes (MWCNTs).
[0011] In a further embodiment, the present application includes an alkali
metal-promoted trimetallic catalyst for higher alcohol synthesis from
synthesis
gas, the catalyst comprising Co, Rh and Mo. In an embodiment of the
application the alkali metal is K and is present in an amount of about 8 wt%
to
about 10 wt%. In a further embodiment, the trimetallic catalyst comprises
about
3.5 wt% to about 7 wt% Co, about 0.5 wt% to about 2.5 wt% Rh and about 14
wt% to about 16 wt% Mo. In a further embodiment, the catalyst of the present
application, comprises about 9 wt% K, about 4.5% Co, about 1.5 wt% Rh and
about 15 wt% Mo, the remainder being primarily the carbon-based support.
[0012] In an embodiment of the application, the catalyst comprises,
consists essentially of, or consists of, K, Co, Rh and Mo, on a carbon based
support.
[0013] It is an embodiment of the application that the carbon-based
support is MWCNTs. MWCNTs display unique properties such as
meso/macroporous structures that mitigate transport limitations, and provide
uniform and straight pores that allow greater metal dispersion, high
mechanical
strength, and thermal conductivity.
[0014] In another embodiment, the catalysts of the application are
prepared by impregnation using an incipient wetness impregnation method. For
example, metal precursors dissolved in aqueous solutions are used to
impregnate the support, followed by drying and stabilizing. In an embodiment,
the support is first impregnated with an aqueous solution of the alkali metal
salt,
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followed by drying and stabilizing. Then the support is further impregnated
with
precursors for M1, M2 and M3 followed by drying and stabilizing. It is an
embodiment of the application that the catalyst is used in its sulfided state
for
higher alcohol synthesis from synthesis gas. Sulfidation of the catalyst is
performed, for example by treating the catalyst with an H2S/H2 gas mixture.
[0015] In an embodiment of the present application, the particle size of the
catalysts is about 140 m to about 220 m.
[0016] The present application also includes a process for producing
higher alcohols from synthesis gas, the method comprising reacting the gas
with
a catalyst of the present application under conditions for the formation of
higher
alcohols.
[0017] Other features and advantages of the present application will
become apparent from the following detailed description. It should be
understood,
however, that the detailed description and the specific examples while
indicating
preferred embodiments of the application are given by way of illustration
only,
since various changes and modifications within the spirit and scope of the
application will become apparent to those skilled in the art from this
detailed
description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The present application will now be described in greater detail with
reference to the drawings in which:
[0019] Figure 1 is an SEM image of an exemplary MWCNT supported
catalyst of the application.
[0020] Figure 2 is a TEM image of an exemplary MWCNT supported
catalyst of the application.
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[0021] Figure 3 shows XRD patterns of exemplary catalysts in oxidized
form a. Rh-Mo-K/MWCNT; b. 4.5 wt % Co- Rh-Mo-K/MWCNT; c. 6 wt % Co-Rh-
Mo-K/MWCNT; d. 4.5 wt % Co- Rh-Mo-K /AC; e. 6 wt % Co- Rh-Mo-K/AC.
[0022] Figure 4 shows XRD patterns of exemplary catalysts in sulfided
form a. Rh-Mo-K/MWCNT; b. 4.5 wt % Co- Rh-Mo-K/MWCNT; c. 6 wt % Co-Rh-
Mo-K/MWCNT; d. 4.5 wt % Co- Rh-Mo-K /AC; e. 6 wt % Co- Rh-Mo-K/AC.
[0023] Figure 5 shows H2 - TPR profiles of exemplary catalysts: a. Rh-Mo-
K/MWCNT; b. 4.5 wt.% Co- Rh-Mo-K/MWCNT; c. 6 wt.% Co-Rh-Mo-K/MWCNT;
d. 4.5 wt.% Co- Rh-Mo-K /AC; e. 6 wt.% Co- Rh-Mo-K/AC.
[0024] Figure 6 is a graph showing % CO Conversion with time on stream
for exemplary catalysts: a. 4.5 wt.% Co- Rh-Mo-K/AC; b. 6 wt.% Co- Rh-Mo-K
/AC; c. Rh-Mo-K/MWCNT; d. 4.5 wt.% Co- Rh-Mo-K/MWCNT; e. 6 wt.% Co-Rh-
Mo-K/MWCNT; (wt. of the cat. = 2 g, P = 8.3 MPa, T = 320 C, GHSV = 3.6
m3(STP)/(kg of cat.)/h, H2/CO molar ratio = 1).
[0025] Figure 7 is a graph showing the change of % CO conversion and
STY of total alcohols and hydrocarbons with temperature for the exemplary
MWCNT-supported alkali-modified trimetallic catalyst promoted with 4.5 wt% Co
(wt. of the cat. = 2 g, P = 8.3 MPa, GHSV = 3.6 m3 (STP)/(kg of cat.)/h, H2 to
CO
molar ratio = 1).
[0026] Figure 8 is a graph showing the selectivities of methanol, ethanol,
higher alcohols, and total alcohols with temperature for the exemplary MWCNT-
supported alkali-modified trimetallic catalyst promoted with 4.5 wt% Co (wt.
of the
cat. = 2 g, P = 8.3 MPa, GHSV = 3.6 m3 (STP)/(kg of cat.)/h, H2 to CO molar
ratio
= 1).
[0027] Figure 9 is a graph showing the change of % CO conversion and
STY of total alcohols and hydrocarbons with pressure for the exemplary
MWCNT-supported alkali-modified trimetallic catalyst promoted with 4.5 wt% Co
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(wt. of the cat. = 2 g, T = 320 C, GHSV = 3.6 m3 (STP)/(kg of cat.)/h, H2 to
CO
molar ratio = 1)
[0028] Figure 10 is a graph showing the selectivities of methanol, ethanol,
higher alcohols, and total alcohols with pressure for the exemplary MWCNT-
supported alkali-modified trimetallic catalyst promoted with 4.5 wt% Co (wt.
of the
cat. = 2 g, T = 320 C, GHSV = 3.6 m3 (STP)/(kg of cat./h), H2 to CO molar
ratio =
1).
[0029] Figure 11 shows a reaction scheme for higher alcohols synthesis
using the CO insertion mechanism.
[0030] Figure 12 shows XRD patterns of exemplary catalysts in sulfide
form a. Mo-K/MWCNT; b. Co-Mo-K/MWCNT; c. Rh-Mo-K/MWCNT; d. Co-Rh-
Mo-K/MWCNT; e. Co-Rh-Mo-K/MWCNT.
[0031] Figure 13 shows an overview of S K-edge and Mo L3-edge XANES
spectra of various exemplary catalysts.
[0032] Figure 14 shows S K-edge XANES spectra of exemplary K-
modified MoS2 catalysts.
[0033] Figure 15 shows Mo L3-edge XANES spectra of exemplary K-
modified MoS2 catalysts.
[0034] Figure 16 shows linear combination fitting of the Mo L3-edge
spectra of the exemplary catalyst Mo-K/MWCNT
[0035] Figure 17 N2 adsorption-desorption isotherms of exemplary pure
supports a. AC-Darco; b. AC-RX3 extra; c. AC-Fluid coke; d. AC-CGP super; e.
MWCNT.
[0036] Figure 18 shows N2 adsorption-desorption isotherms of exemplary
pure supports a. AC-Darco; b. AC-RX3 extra; c. AC-Fluid coke; d. AC-CGP super;
e. MWCNT.
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[0037] Figure 19 shows XRD patterns of exemplary catalysts in oxidized
form a. AC-Darco; b. AC-RX3 extra; c. AC-Fluid coke; d. AC-CGP super; e.
MWCNT.
[0038] Figure 20 shows TEM images of exemplary supported catalysts a.
AC-Darco; b. AC-RX3 extra; c. AC-Fluid; d. AC-CGP super; e. MWCNT.
[0039] Figure 21 shows CO Conversion (%) with time-on-stream for
exemplary catalyst: a. AC-Darco; b. AC-RX3 extra; c. AC-Fluid coke; d. AC-CGP
super; e. MWCNT (wt. of the cat. = 2 g, P = 8.3 MPa, T = 330 C, GHSV = 3.6 m3
(STP)/(kg of cat.)/h, Hz/CO molar ratio = 2)
[0040] Figure 22 shows the effects of the temperature, pressure, and gas
hourly space velocity on % CO conversion over the exemplary Co (4.5 wt%)-Rh
(1.5 wt%)-Mo (15 wt%)-K (9 wt%)/MWCNT catalyst; a. and b. 3-D surface
responses, c. Perturbation plot where A = -1 + (T - 275)/37.5, B = -1 + (P -
800)/300 and C = -1 + (GHSV - 2.4)/1; d. Quality of fit.
[0041] Figure 23 shows the effects of the temperature, pressure, and gas
hourly space velocity on methanol STY over the exemplary Co (4.5 wt%)-Rh (1.5
wt%)-Mo (15 wt%)-K (9 wt%)/MWCNT catalyst; a. and b. 3-D surface responses,
c. Perturbation plot where A = -1 + (T - 275)/37.5, B = -1 + (P - 800)/300 and
C =
-1 + (GHSV - 2.4)/1.
[0042] Figure 24 shows the effects of the temperature, pressure, and gas
hourly space velocity on ethanol STY over the exemplary Co (4.5 wt%)-Rh (1.5
wt%)-Mo (15 wt%)-K (9 wt%)/MWCNT catalyst; a. and b. 3-D surface responses,
c. Perturbation plot where A = -1 + (T - 275)/37.5, B = -1 + (P - 800)/300 and
C =
-1 + (GHSV - 2.4)/1.
[0043] Figure 25 shows the effects of the temperature, pressure, and gas
hourly space velocity on total alcohol STY over the exemplary Co (4.5 wt%)-Rh
(1.5 wt%)-Mo (15 wt%)-K (9 wt%)/MWCNT catalyst; a. and b. 3-D surface
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responses, c. Perturbation plot where A = -1 + (T - 275)/37.5, B = -1 + (P -
800)/300 and C = -1 + (GHSV - 2.4)/1.
[0044] Figure 26 shows the effects of the temperature, pressure, and gas
hourly space velocity on hydrocarbon STY over the exemplary Co (4.5 wt%)-Rh
(1.5 wt%)-Mo (15 wt%)-K (9 wt%)/MWCNT catalyst; a. and b. 3-D surface
responses, c. Perturbation plot where A = -1 + (T - 275)/37.5, B = -1 + (P -
800)/300 and C = -1 + (GHSV - 2.4)/1.
[0045] Figure 27 shows the effects of the temperature, pressure, and gas
hourly space velocity on ethanol selectivity over the exemplary Co (4.5 wt%)-
Rh
(1.5 wt%)-Mo (15 wt%)-K (9 wt%)/MWCNT catalyst; a. and b. 3-D surface
responses, c. Perturbation plot where A = -1 + (T - 275)/37.5, B = -1 + (P -
800)/300 and C = -1 + (GHSV - 2.4)/1.
[0046] Figure 28 shows the effect of the H2 to CO molar ratio on % CO
conversion, hydrocarbons, and CO2 STY over the exemplary Co-Rh-Mo-
K/MWCNTs catalyst at 330 C, 1320 psig, and 3.8 m3 (STP)/(kg of cat.)/h.
[0047] Figure 29 shows the effect of the H2 to CO molar ratio on methanol,
ethanol, higher alcohols, and total alcohols STY over the exemplary Co-Rh-Mo-
K/MWCNT catalyst at 330 C, 1320 psig, and 3.8 m3 (STP)/(kg of cat.)/h.
[0048] Figure 30 shows the effect of the H2 to CO molar ratio on methanol,
ethanol, higher alcohols, and total alcohols selectivity over the exemplary Co-
Rh-
Mo-K/MWCNT catalyst at 330 C, 1320 psig, and 3.8 m3 (STP)/(kg of cat.)/h.
[0049] Figure 31 shoes an exemplary experimental set-up for higher
alcohols synthesis from synthesis gas.
[0050] Figure 32 shows the effect of particle size on % CO conversion; a.
275 C; b. 300 C; c. 325 C; d. 350 C for an exemplary K-promoted Co-Rh-
Mo/MWCNT catalyst (wt. of the cat. = 2 g, P = 9.1 MPa, GHSV = 3.6 m3
(STP)/(kg of cat.)/h, H2 to CO molar ratio = 1.25).
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[0051] Figure 33 shows the effect of particle size on total alcohols STY a.
275 C; b. 300 C; c. 325 C; d. 350 C, for an exemplary k-promoted Co-Rh-
Mo/MWCNT catalyst (wt. of the cat. = 2 g, P = 9.1 MPa, GHSV = 3.6 m3
(STP)/(kg of cat.)/h, H2 to CO molar ratio = 1.25).
[0052] Figure 34 shows the effect of flow rate on % CO conversion for an
exemplary K-promoted Co-Rh-Mo/MWCNT catalyst (wt. of the cat. = 2 g, T =
325 C, P = 9.1 MPa, H2 to CO molar ratio = 1.25, Average particle size = 0.179
mm ml/min).
[0053] Figure 35 shows comparison plots for observed methanol formation
rate for an exemplary K-promoted Co-Rh-Mo/MWCNT catalyst.
[0054] Figure 36 shows comparison plots for observed ethanol formation
rate for an exemplary K-promoted Co-Rh-Mo/MWCNT catalyst.
[0055] Figure 37 shows comparison plots for observed higher alcohols
formation rate for an exemplary K-promoted Co-Rh-Mo/MWCNT catalysts
[0056] Figure 38 shows comparison plots for observed hydrocarbons
formation rate for an exemplary K-promoted Co-Rh-Mo/MWCNT catalyst.
[0057] Figure 39 shows comparison plots for observed carbon dioxide
formation rate for an exemplary K-promoted Co-Rh-Mo/MWCNT catalyst.
[0058] Figure 40 shows a TEM image of an exemplary MWCNT-supported
catalyst; a. Fresh catalyst, b. Spent catalyst.
[0059] Figure 41 shows a TEM image of an exemplary activated carbon-
supported catalyst; a. Fresh catalyst, b. Spent catalyst.
[0060] Figure 42 shows XRD patterns of an exemplary MWCNT-supported
catalyst; a. Fresh catalyst, b. Sulfided catalyst, c. Spent catalyst.
[0061] Figure 43 shows XRD patterns of an exemplary activated carbon-
supported catalyst; a. Fresh catalyst, b. Sulfided catalyst, c. Spent
catalyst.
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[0062] Figure 44 shows H2 - TPR profiles of an exemplary MWCNT-
supported catalyst; a. Fresh catalyst, b. Spent catalyst.
[0063] Figure 45 shows H2 - TPR profiles of an exemplary activated
carbon-supported catalyst; a. Fresh catalyst, b. Spent catalyst.
[0064] Figure 46 shows TG profiles of an exemplary MWCNT-supported
catalyst; a. Fresh catalyst, b. Spent catalyst.
[0065] Figure 47 shows TG profiles of an exemplary activated carbon-
supported catalyst; a. Fresh catalyst, b. Spent catalyst.
[0066] Figure 48 shows % CO conversion with time-on-stream; a. an
exemplary MWCNT-supported catalyst, b. an exemplary activated carbon-
supported catalyst (wt. of the cat. = 2 g, P = 9.1 MPa, T = 330 C, GHSV = 3.8
m3(STP)/h/(kg of cat.)/h, H2 to CO molar ratio = 1.25).
[0067] Figure 49 shows total alcohols STY with time-on-stream; a. an
exemplary MWCNT-supported catalyst, b. an exemplary activated carbon-
supported catalyst (wt. of the cat. = 2 g, P = 9.1 MPa, T = 330 C, GHSV = 3.8
m3(STP)/h/(kg of cat.)/h, H2/CO molar ratio = 1.25).
[0068] Figure 50 shows total hydrocarbons STY with time-on-stream; a. an
exemplary MWCNT-supported catalyst, b. an exemplary activated carbon-
supported catalyst (wt. of the cat. = 2 g, P = 9.1 MPa, T = 330 C, GHSV = 3.8
m3(STP)/h/(kg of cat.)/h, H2/CO molar ratio = 1.25).
[0069] Figure 51 shows water-gas-shift reaction rate with time-on-stream;
a. an exemplary MWCNT-supported catalyst, b. an exemplary activated carbon-
supported catalyst (wt. of the cat. = 2 g, P = 9.1 MPa, T = 330 C, GHSV = 3.8
m3(STP)/h/(kg of cat.)/h, H2/CO molar ratio = 1.25).
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DETAILED DESCRIPTION OF THE APPLICATION
1. Definitions
[0070] Unless otherwise indicated, the definitions and embodiments
described in this and other sections are intended to be applicable to all
embodiments and aspects of the disclosure herein described for which they are
suitable as would be understood by a person skilled in the art.
[0071] As used in this application, the singular forms "a", "an" and "the"
include plural references unless the content clearly dictates otherwise. For
example, an embodiment including "a catalyst" should be understood to present
certain aspects with one catalyst, or two or more additional catalysts.
[0072] In embodiments comprising an "additional" or "second" component,
such as an additional or second catalyst, the second component as used herein
is chemically different from the other components or first component. A
"third"
component is different from the other, first, and second components, and
further
enumerated or "additional" components are similarly different.
[0073] The term "suitable" as used herein means that the selection of the
particular compound or conditions would depend on the specific synthetic
manipulation to be performed, and the identity of the molecule(s) to be
transformed, but the selection would be well within the skill of a person
trained in
the art. All process/method steps described herein are to be conducted under
conditions sufficient to provide the desired product. A person skilled in the
art
would understand that all reaction conditions, including, for example,
reaction
solvent, reaction time, reaction temperature, reaction pressure, reactant
ratio and
whether or not the reaction should be performed under an anhydrous or inert
atmosphere, can be varied to optimize the yield of the desired product and it
is
within their skill to do so.
[0074] In understanding the scope of the present disclosure, the term
"comprising" and its derivatives, as used herein, are intended to be open
ended
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terms that specify the presence of the stated features, elements, components,
groups, integers, and/or steps, but do not exclude the presence of other
unstated
features, elements, components, groups, integers and/or steps. The foregoing
also applies to words having similar meanings such as the terms, "including",
"having" and their derivatives. The term "consisting" and its derivatives, as
used
herein, are intended to be closed terms that specify the presence of the
stated
features, elements, components, groups, integers, and/or steps, but exclude
the
presence of other unstated features, elements, components, groups, integers
and/or steps. The term "consisting essentially of", as used herein, is
intended to
specify the presence of the stated features, elements, components, groups,
integers, and/or steps as well as those that do not materially affect the
basic and
novel characteristic(s) of features, elements, components, groups, integers,
and/or steps.
[0075] Terms of degree such as "substantially", "about" and
"approximately" as used herein mean a reasonable amount of deviation of the
modified term such that the end result is not significantly changed. These
terms
of degree should be construed as including a deviation of at least 5% of the
modified term if this deviation would not negate the meaning of the word it
modifies.
[0076] The term "wt%" as used herein, unless otherwise indicated, means
percent by weight of the entire catalyst including the support.
[0077] The term "higher alcohols" as used herein refers to hydrocarbon
alcohols with a carbon number greater than 2 (C2+ alcohols), including for
example, ethanol, propanol, butanol, pentanol and the like.
[0078] The term "alkali metal" as used herein refers to an element in
Group I (modern IUPAC naming) of the periodic table, including lithium (Li),
sodium (Na), potassium (K), rubidium (Rb) and cesium (Cs). In an embodiment,
the alkali metal is K.
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[0079] The term "synthesis gas" as used herein means a gas comprising,
as its major components, carbon monoxide (CO) and hydrogen (H2). For
example synthesis gas may comprise 5-50% CO and 5-50% H2. Synthesis gas
may further comprise hydrogen sulfide (H2S), carbon dioxide (CO2), water
(H2O),
methane (CH4), higher hydrocarbons, nitrogen (N2) and other contaminants.
Synthesis gas is available, for example, from the gasification of biomass (a
thermal-chemical process that uses partial oxidation to convert organically
derived feedstock into synthesis gas); gasification of hydrocarbonaceous
materials such as coal, high specific gravity oils, or natural gas; as a by-
product
of partial combustion cracking of hydrocarbons; by steam reforming of liquid
or
gaseous hydrocarbons; through the water-gas shift reaction; or some
combination of these. The CO and H2 may also be generated separately and
combined.
[0080] The term "dry" or "drying" as used herein refers to the removal of
essentially all of the solvent or solvents from a material. Suitable
conditions for
drying the supports or catalysts of the present application will be those
sufficient
for driving off essentially all of the solvent or solvents used in a previous
application step.
II. Catalysts of the Application
[0081] Multi-walled carbon nanotubes (MWCNTs) and activated carbon
were used as supports for Co-promoted, alkali-modified, Rh-Mo catalysts. The
catalysts were extensively characterized in both oxide and sulfide phases.
Diffraction peaks were observed in the X-ray diffraction (XRD) patterns of the
sulfided alkali-modified trimetallic catalysts, due to the characteristic
reflections of
the K-Mo-S mixed phase. H2-temperature programmed reduction (TPR) profiles
showed that the reduction behavior of metal species was improved with the
addition of Co. The activated carbon-supported trimetallic catalysts showed
less
activity and selectivity compared to the MWCNT-supported catalyst, and metal
dispersions were higher on the MWCNT-supported catalysts. The MWCNT-
CA 02739142 2011-05-05
16
supported, alkali-promoted trimetallic catalyst with 4.5 wt% Co showed the
highest total alcohols yield of 0.244 g/(g of cat.)/h, ethanol selectivity of
20.1%,
and higher alcohols selectivity of 31.4% at 320 C and 8.28 MPa using a gas
hourly space velocity (GHSV) of 3.6 m3 (STP)/(kg of cat.)/h. A maximum total
alcohol yield of 0.261 g/(g of cat.)/h and selectivity of 42.9% were obtained
on the
4.5 wt % Co-Rh-Mo-K/MWCNT catalyst, at a temperature of 330 C. The total
alcohol yield increased from 0.163 to 0.256 g/(g of cat.)/h with increased
pressure from 5.52 MPa (800 psig) to 9.65 MPa (1400 psig) over the 4.5 wt%
Co-Rh-Mo-K/MWCNT catalyst.
[0082] Accordingly, the present application includes a catalyst comprising
the Formula (I):
A-M'-M2-M3 (I)
wherein A is an alkali metal;
M' is selected from Co, Ni and Fe;
M2 is selected from Rh, Ru and Pd; and
M3 is selected from Mo;
wherein the catalyst is supported on a carbon-based material.
[0083] In an embodiment the catalyst comprises the Formula A-Co-Rh-Mo,
wherein A is an alkali metal, and the catalyst is supported on a carbon-based
support selected from activated carbon and multi-walled carbon nano-tubes
(MWCNTs). In an embodiment of the application, the alkali metal is K.
[0084] In the catalysts of the application, M1 is one of the closely related
transition metals, Co, Ni or Fe, suitably Co and M2 is one of the closely
related
precious transition metals, Rh, Ru or Pd, suitably Rh.
[0085] In a further embodiment, the present application includes an alkali
metal-promoted trimetallic catalyst for higher alcohol synthesis from
synthesis
gas, the catalyst comprising Co, Rh and Mo. In an embodiment of the
application the alkali metal is K and is present in an amount of about 8 wt%
to
CA 02739142 2011-05-05
17
about 10 wt%, or about 9 wt%. In a further embodiment, the trimetallic
catalyst
comprises about 3.5 wt% to about 7 wt%, or about 4.5 wt%, Co, about 0.5 wt% to
about 2.5 wt%, or about 1.5 wt%, Rh and about 14 wt% to about 16 wt%, or
about 15 wt%, Mo. In a further embodiment, the catalyst of the present
application, comprises about 9 wt% K, about 4.5% Co, about 1.5 wt% Rh and
about 15 wt% Mo, the remainder being primarily the carbon-based support.
[0086] In an embodiment of the application, the catalyst comprises,
consists essentially of, or consists of K, Co, Rh and Mo, on a carbon based
support.
[0087] It is an embodiment of the application that the carbon-based
support is MWCNTs. MWCNTs display unique properties such as
meso/macroporous structures that mitigate transport limitations, and provide
uniform and straight pores that allow greater metal dispersion, high
mechanical
strength, and thermal conductivity. Prior to impregnation with metals, it is
an
embodiment that the support is treated with acid, for example nitric acid
(HNO3),
including about 30% HNO3, followed by washing, for example with distilled
water,
to remove residual acid and drying, for example at about 100 C to about 150
C,
or about 120 C, for a time sufficient to dry the support.
[0088] In another embodiment, the catalysts of the application are
prepared by impregnation using an incipient wetness impregnation method. For
example, metal precursors dissolved in aqueous solutions are used to
impregnate the support, followed by drying and stabilizing. For example, an
acid
treated support is first impregnated with an aqueous solution comprising
required
amounts of the alkali metal salt, for example, potassium carbonate (K2CO3),
followed by drying, for example at about 100 C to about 150 C, or about 120
C, for a time sufficient to dry the support, and stabilizing, for example in
flow of
an inert gas, such as Ar, at a flow rate of about 25 to 75 ml/min or about 50
ml/min, at a temperature of about 250 C to about 400 C, or about 300 C, at
a
heating rate of about 5-20 C/min, or about 10 C/min, for about 2 to about 10
CA 02739142 2011-05-05
18
hours, or about 4 hours. The support is then further impregnated with aqueous
solutions containing the required amounts of the M1, M2 and M3 precursors
followed by drying, for example at about 100 C to about 150 C, or about 120
C,
for a time sufficient to dry the support, and stabilizing, for example in flow
of an
inert gas, such as Ar, at a flow rate of about 25 to 75 ml/min or about 50
ml/min,
at a temperature of about 300 C to about 550 C, or about 450 C, at a
heating
rate of about 5-20 C/min, or about 10 C/min, for about 6 to about 24 hours,
or
about 12 hours. In an embodiment, the support is first impregnated with an
aqueous solution of the alkali metal salt, followed by drying and stabilizing.
Then
the support is further impregnated with precursors for M1, M2 and M3 followed
by
drying and stabilizing.
[0089] The impregnation will typically be carried out until the catalyst
support has absorbed a volume of impregnating solution equal to at least about
100% of its calculated pore volume, suitably to where conditions of incipient
wetness are attained. By incipient wetness is meant that the support has
adsorbed an amount of solution generally equivalent to its calculated pore
volume. Pore volume is a discernible quantity that can be measured directly or
indirectly by known techniques such as porosimetry. The volume of impregnating
solution contemplated will vary from 10% to 1000% of the calculated pore
volume
of the catalyst. Suitably, the volume of treatment solution will be from 30%
to
200%, most preferably from about 70% to 100% of the calculated pore volume of
the catalyst.
[0090] The impregnating solution will remain in contact with the support for
from 1 minute to 24 hours, suitably from about 5 to 120 minutes. The time
required for the treatment will vary depending on factors such as the metal
loading of the support being treated, the quantity thereof, the composition
and
volume of the impregnating solution, the reactor configuration and the like.
The
treatment is carried out at a temperature from about 0 C to about 100 C, or
CA 02739142 2011-05-05
19
from room temperature, i.e. 20-25 C, to about 80 C. The pressure is not
particularly critical with atmospheric pressure being suitable.
[0091] Once the support has absorbed the desired volume of impregnating
solution, it undergoes oxidation in the presence of the impregnating solution.
It is
an embodiment of the application that the catalyst is used in its sulfided
state for
higher alcohol synthesis from synthesis gas. Sulfidation of the catalyst is
performed, for example by treating the oxide catalyst with H2S. In an
embodiment sufidation is carried out at the same time as the catalyst is
activated
by reduction prior to catalyst use to convert synthesis gas to higher
alcohols. In
this embodiment the oxide catalyst is treated with an H2S/H2 gas mixture, for
example about 5 mole% to about 20 mole%, or about 10 mole% H2S in H2 gas,
at a temperature of about 300 C to about 550 C, or about 450 C, at a
heating
rate of about 1-5 C/min, or about 2 C/min, for about 2 to about 10 hours, or
about 4 hours.
[0092] In an embodiment of the application, the precursor compound for K
is potassium carbonate (K2CO3), the precursor compound for Mo is ammonium
heptamolybdate tetrahydrate ((NH4)6Mo7O24), the precursor compound for Co is
cobalt acetate tetrahydrate (Co(CH3000)2), and the precursor for Rh is rhodium
chloride hydrate (RhC13), although a person skilled in the art would
appreciate
that other precursor compounds can be used in place of these compounds
without deviating from the scope of the present application. These precursor
compounds are commercially available.
[0093] In an embodiment of the present application, the average particle
size of the catalysts is about 140 m to about 220 pm, or about 147 m to
about
210 m.
[0094] In another embodiment of the present application there is included
catalyst particles that comprise, consist essentially of, or consist of, an
alkali-
modifier, a Co-promoter, and a Rh-Mo sulfide catalyst wherein the particles
have
CA 02739142 2011-05-05
an average particle size of about 140 m to about 220 m, or about 147 m to
about 210 m.
[0095] The MWCNT-supported alkali-promoted Co-Rh-Mo trimetallic
catalysts of the application, showed enhanced CO hydrogenation capability,
compared to that of corresponding MWCNT-supported alkali-promoted Rh-Mo
bimetallic catalyst. With the addition of 4.5 wt % Co on the MWCNT-supported
1.5 wt % Rh, 15 wt % Mo, and 9 wt % K catalyst, the total alcohols STY
increased to 0.244 g/(g of cat.)/h and the total hydrocarbons STY decreased to
0.251 g/(g of cat.)/h. The methanol, ethanol, and higher alcohols
selectivities,
respectively, increased from 5.4%, 16.0%, and 24.6% over the alkali-promoted
bimetallic Rh-Mo/MWCNT catalyst to 6.7%, 20.1%, and 31.4% on the MWCNT-
supported trimetallic catalyst promoted with 4.5 wt % Co. From the CO
chemisorption results, it was observed that incorporation of 4.5 wt % Co to
the
alkali-modified bimetallic Rh-Mo catalyst supported on MWCNTs increased the
CO uptake from 135 to 237 pmole/(g of cat.). Also, Co promotion to Rh-Mo-
K/MWCNT catalyst increased the metal dispersion from 39.5 to 49.8% favoring
the formation of fine particles. These results, coupled with XRD data, confirm
that
incorporating Co metal increased the number of active sites responsible for
the
formation of alcohols.
Ill. Processes of the Application
[0096] The catalysts of the present application are useful for the
conversion of synthesis gas to alcohols (in particular higher alcohols), in
the so-
called Fischer-Tropsch reaction.
[0097] The present application therefore includes a process for producing
higher alcohols from synthesis gas, the process comprising reacting the gas
with
a catalyst of the application under conditions for the formation of higher
alcohols.
[0098] In an embodiment of the present application the conditions for the
formation of higher alcohols comprise a temperature of about 300 C to about
CA 02739142 2011-05-05
21
350 C, or about 330 C; a pressure of about 5.5 Mpa to about 10 MPa, or about
8.0 MPa to about 9.0 MPa; and a gas hourly space velocity (GHSV) of about 2.5
m3 (STP)/(kg of cat)/h to about to about 4.5 m3 (STP)/(kg of cat)/h, or about
3.8
m3 (STP)/(kg of cat)/h.
[0099] In a further embodiment of the present application the molar ratio of
H2:CO in the synthesis gas is about 1:1 to about 1.5:1, or about 1.25:1.
[00100] In accordance with the present application, and as described above,
the catalysts of the present application are activated and sulfided in a
single step
prior to use to convert synthesis gas to higher alcohols. In this embodiment
the
oxide catalysts are treated with an H2S/H2 gas mixture, for example about 5
mole% to about 20 mole%, or about 10 mole% H2S in H2 gas; at a temperature of
about 300 C to about 550 C, or about 450 C; at a heating rate of about 1-5
C/min, or about 2 C/min; for about 2 to about 10 hours, or about 4 hours.
[00101] It is a further optional step within the scope of the present
application to passivate the treated catalyst after the activation/sulfidation
with
H2S/H2 gas mixture has been carried out. The passivation may be carried out by
contacting the catalyst with a gas containing carbon monoxide, or carbon
monoxide and hydrogen, under conditions such that carbon monoxide does not
significantly decompose and is not hydrogenated to a material degree. Such
conditions, for example, would be a temperature below about 150 C, or about
25
C to about 100 C, and pressure below about 20 atm, or about 1 to about 10 atm
and the GHSV would be from about 1 V/HrN to about 1,000 V/HrN, or about 10
V/HrN to about 500 V/HrN, expressed as standard volumes of the gas or gas
mixtures (25 C, 1 atm) per hour per volume of catalyst, respectively. It will
be
appreciated that some decomposition or hydrogenation, respectively, of the
carbon monoxide may take place regardless of the precautions taken by the
operator. However, it has been found that, typically, significant
decomposition/hydrogenation will not take place wherein the concentration of
carbon monoxide or carbon monoxide and hydrogen in the feed gas does not
CA 02739142 2011-05-05
22
exceed about 5% by volume. Other passivating agents include, for example,
traces of oxygen or carbon dioxide.
[00102] In another embodiment the process of the application is carried out
as a continuous process with a catalyst of the present application in a
suitable
reactor, for example a fixed bed reactor, a slurry reactor, a loop reactor, a
bubble-column reactor or a fluid-bed reactor. Accordingly, the present
application also includes a reactor comprising a catalyst of the application.
[00103] Effluent reactant gases and liquids from the process may be
separated and recycled, if desired, for further alcohol synthesis. Industrial
methods of collecting the products are well known and include fractional
distillation and the like. Auxiliary equipment is conventional and known to
those
skilled in the art.
The following non-limiting examples are illustrative of the present
application:
EXAMPLES
Example 1: Preparation and Characterization of K-Promoted Trimetallic
Catalysts
Materials and Methods
(a) Preparation of K -promoted trimetallic catalysts
[00104] MWCNTs (M. K. Nano, surface area 178 m2/g, pore volume 0.54
cm3/g) and activated carbon (Aldrich, surface area 655 m2/g, pore volume 0.93
cm3/g) were used as supports for the preparation of the catalysts. Prior to
impregnation, the support was treated with 30% HNO3 reflux at 100 C overnight,
washed with distilled water several times, and dried at 120 C for 6 h. The
oxide
samples were prepared by the sequential pore volume impregnation method
using ammonium heptamolybdate tetrahydrate (Sigma-Aldrich), potassium
carbonate (Aldrich), cobalt acetate tetrahydrate (Alfa-Aesar), and rhodium
CA 02739142 2011-05-05
23
chloride hydrate (Aldrich) as precursors for Mo, K, Co, and Rh, respectively.
At
the first step, the support was impregnated with an aqueous solution of K2CO3,
followed by drying at 120 C for 2 h and stabilizing in an argon flow of 50
ml/min
at 300 C, at a heating rate of 10 C/min for 4 h. The support was further
impregnated with aqueous solutions containing the required amounts of
(NH4)6Mo7O24, Co(CH3COO)2, and RhCI3 followed by drying at 120 C for 2 h and
stabilizing in an argon flow of 50 ml/min at 450 C, at a heating rate of 10
C/min
for 12 h. The sulfide samples were obtained by heat-treating the oxide
precursors
in a flow of 10 mole % H2S in H2 gas at 450 C, at a heating rate of 2 C/min
for 4
h.
(b) Characterization of K-promoted trimetallic catalysts
[00105] The surface area, pore volume, and average pore diameter of oxide
samples were measured by N2 physisorption at 77 K using a Micromeritics ASAP
2000. Approximately 0.2 g of sample was used for each analysis. The moisture
and other adsorbed gases present in the sample were removed before analysis
by degassing the sample at 200 C for 2 h under 66.7 Pa (500 mmHg). The
sample was then evacuated at 2.67 Pa (20 Nm Hg) before N2 adsorption.
[00106] The content of Mo, Co, and Rh of the oxide catalysts was
determined using a Perkin-Elmer ELAN 5000 inductively coupled plasma mass
spectroscopy (ICP-MS) instrument.
[00107] Powder X-ray diffraction (XRD) analysis patterns of oxide and
sulfide forms of samples were recorded on a Rigaku X-ray diffraction
instrument
with nickel-filtered Cu KR radiation (A = 0.1541 nm). Each sample was scanned
at a rate of 0.05 /s, with 26 varying from 10 to 80 . To obtain the XRD
patterns in
sulfided form, the catalysts were first sulfided for 6 h at 450 C, at a
heating rate
of 2 C/min using a gaseous mixture containing 10 mole % H2S in H2 at a flow
rate of 50 ml/min. After sulfidation, the catalysts were cooled to room
CA 02739142 2011-05-05
24
temperature in a flow of He and the sample was transferred to sample holders
under protection of He.
[00108] Carbon monoxide was used as a probe molecule to determine the
number of accessible surface metal atoms present on the sulfided catalysts.
The
CO uptake (Nmole/g of cat.) measured from CO chemisorption is equivalent to
the number of active metal atoms that are accessible to the reactant
molecules.
The stoichiometric coefficient (CO to metal ratio) of 1 was used, and the
extent of
reduction was assumed to be 100% in metal dispersion calculations. The carbon
monoxide uptake on the sulfided catalysts was measured using the Micromeritics
ASAP 2000 instrument. Prior to the CO chemisorption measurement, 0.2 g of
sample was sulfided in situ, using 10 mole % H2S in H2 at 400 C for 4 h. The
sample was then evacuated at 120 C until the static pressure remained less
than
6.6 x 10"4 Pa. Chemisorption was performed by passing pulses of CO over the
sample to measure the total gas uptake at 35 C.
[00109] To study the reducibility of the metal oxides in the catalysts,
temperature programmed reduction (TPR) profiles of the catalysts were
performed. For each analysis, approximately 0.2 g of sample was used, which
was first purged in a flow of argon at 170 C to remove traces of water, and
then
cooled to 40 C. The TPR of each sample was performed using a 3.1 mole % H2
in He stream at a flow rate of 30 mL/min at atmospheric pressure using a
CHEMBET 3000 TPD-TPR analyzer equipped with a thermal conductivity
detector, heating at a linearly programmed rate of 10 C/min up to 800 C.
[00110] The oxide samples were characterized by scanning electron
microscopy (SEM) using a Phillips SEM-505 scanning electron microscope
operating at 300 kV in SE display mode. The outer diameter of the nanotubes
was measured using Digital micrograph software (version 3.6.5, Gatan Inc.).
[00111] The morphology of the oxide samples was characterized by
transmission electron microscopy (TEM) investigations, using a Philips CM20
CA 02739142 2011-05-05
(100 kV) transmission electron microscope equipped with a NARON energy-
dispersive spectrometer with a germanium detector.
(c) Higher alcohols synthesis
[00112] A single-pass tubular downflow fixedbed reactor of 450-mm length
and 22-mm inside diameter made of inconel tube was used to perform higher
alcohols synthesis reactions. The reactor was packed with 2 g of catalyst
diluted
with 12 ml of 90 mesh size silicon carbide and housed in an electric furnace
controlled by a temperature controller. The reactor was pressurized with He to
3.44 MPa (500 psig) and the sulfidation, together with the reduction, was
carried
out for 6 h at 450 C at a heating rate of 2 C/min using a gas mixture
containing
10 mole % H2S in H2 and a flow rate of 50 ml/min. The temperature was then
lowered to the reaction temperature, and the system pressurized to the
reaction
conditions. The feed gas mixture CO (45 mole %), H2 (45 mole %), and Ar (10
mole %) was passed through mass flow controllers and the higher alcohols
synthesis reaction was carried out at steady-state under the reaction
conditions
of 300-340 C, 5.51 (800 psig) to 9.65 MPa (1400 psig), and a gas hourly space
velocity (GHSV) of 3.6 m3 (STP)/(kg of cat.)/h over a period of 24 h. The
product
gas was cooled to 0 C and separated into gas and liquid phases at the reaction
pressure. The CO conversion and other gaseous products were monitored with a
time interval of 1 h. The liquid products were collected at the end of the
reaction
and analyzed with a Varian 3400 gas chromatograph equipped with a capillary
column and a flame ionization detector (FID). The volume and weight of liquid
products were measured to check the mass balance. The gaseous products
were analyzed online on a Shimadzu gas chromatograph through a sampling
valve. Using Ar as an internal standard, the CO conversion was calculated and
the overall mass balance of the reaction was determined. The experiments were
repeated at least twice to check reproducibility and to confirm that the
results
obtained were within the experimental error of 2.5%.
Results and Discussion
CA 02739142 2011-05-05
26
(a) Characterization of K-promoted trimetallic catalysts
[00113] Scanning electron microscopy was used to identify the growth of
the MWCNTs. Figure 1 shows the surface topology of the grown carbon
nanotubes in bundles. The outside diameter of the MWCNTs clearly shows that
the nanotubes are multiwalled and have a structure with several walls of
graphitic
carbons in concentric circles. The nanotubes are found to be tangled. The
outer
diameter of the nanotubes, as measured from the micrograph ranges from 10-30
nm.
[00114] TEM images of the MWCNT-supported catalysts were recorded
and, as shown in Figure 2, revealed that the catalyst particles are well
dispersed
both inside the carbon nanotubes and on the outside of the tube walls. The
carbon nanotubes are multiwalled, with inner diameters in the range of 5-12 nm
and wall thickness in the range of 3 to 8 nm. The particle sizes of the metal
species that are inside and outside of the tubes are in the range of 1-3 nm.
[00115] Table 1 shows the results for surface area, total pore volume, and
average pore diameter of the stabilized catalysts. After acid treatment, the
BET
surface area of the MWCNTs increased from 178 to 220 m2/g, whereas, an
increase from 655 to 676 m2/g was observed in the BET surface area of
activated
carbon. The MWCNT-supported bimetallic (1.5 wt % Rh and 15 wt % Mo)
catalyst promoted with 9 wt % K showed a BET surface area of 77 m2/g and a
total pore volume of 0.30 cm3/g. Increasing the amount of Co from 4.5 to 6 wt
%
decreased the BET surface area of the MWCNT-supported, alkali-promoted
trimetallic catalysts from 68 to 59 m2/g and the total pore volume from 0.24
to
0.20 cm3/g. After impregnating with metal species, a drastic fall in surface
area
over the activated carbon-supported catalysts was observed. A BET surface area
of 97 and 83 m2/g and a total pore volume of 0.16 and 0.11 cm3/g were observed
over the activated carbon-supported, alkali-promoted trimetallic catalysts
that are
promoted with 4.5 and 6 wt %, respectively.
CA 02739142 2011-05-05
27
[00116] The Co, Rh, and Mo contents of the stabilized catalysts measured
by ICP-MS are reported in Table 1, along with the targeted compositions. The
measured contents of the prepared catalysts are slightly lower compared to
targeted values, which may be due to the hygroscopic nature of precursors. For
the activated carbon-based catalysts, the deviation is greater, indicating
that
metal particles are not uniformly dispersed on this support.
[00117] The results of the CO chemisorption measurements are also given
in Table 1. The CO uptake increased from 135 to 237 and 245 Nmole/(g of cat.)
with the incorporation of 4.5 and 6 wt % Co, respectively, to the MWCNT-
supported, alkali-promoted bimetallic Rh-Mo catalyst. This confirms that
MWCNT-supported alkali-promoted Co-Rh-Mo trimetallic catalysts enhanced the
CO hydrogenation capability, compared to that of MWCNT-supported alkali-
promoted Rh-Mo bimetallic catalyst. A metal dispersion of 48% was observed on
the alkali-promoted trimetallic catalyst with 4.5 wt % Co content that was
supported on the MWCNTs. When the Co content was increased to 6 wt % on
the MWCNT-supported, alkali-promoted trimetallic catalyst, the metal
dispersion
decreased to 45%, suggesting that high Co loading (6 wt %) leads to the
formation of large particles. From XRD data, it is seen that amount of Co9S3
species is high at higher Co content (6 wt % Co) in Co-Mo-K/MWCNT catalysts.
Higher Co loading decreases the surface area of the active Co-Mo-S phase
(responsible for the formation of higher alcohols), resulting lower metal
dispersion.44 Metal dispersions of 28% and 26% were observed on the activated
carbon supported alkali-promoted trimetallic catalysts containing 4.5 and 6 wt
%
Co, respectively.
[00118] The XRD patterns of the catalysts in oxidized and sulfided form
were measured and shown in Figures 3 and 4, respectively. The JCPDS
chemical spectra data bank was used to detect the most probable phases
present in the samples, and the results of the possible crystal phases with
their
corresponding reflection planes are given in Table 2.
CA 02739142 2011-05-05
28
[00119] The strong intensity peaks at 20 value of 26.6 are due to the
reflections of the graphite phase present in the MWCNT and activated carbon
supports.41 The characteristic reflections corresponding to the crystalline
structure of MoO3 are observed at 20 value of 40.2 .41. In the oxidized form
of
the MWCNT-supported alkali-promoted bimetallic Rh-Mo catalyst, K-Mo-O mixed
phases exist in several forms. The peaks at 20 values of 19.4 , 28.5 , 29.8 ,
and
30.9 correspond to the characteristic reflections of the K2Mo2O7 phase.45
Other
K-Mo-O phases, such as KMo4O6 (20 = 16.0 and 37.1 ) and K2M07O20 (20 =
23.6 and 53.8 ), also exist on this catalyst.46,47 The diffraction intensity
of the
peaks was greatly reduced with the incorporation of Co, which confirms that
adding the third metal to the alkali-promoted bimetallic Rh-Mo catalysts
improved
the dispersion of the metal species on the support.
[00120] The various diffraction peaks observed in the XRD patterns of oxide
samples are completely removed after sulfidation, and new diffraction peaks
representing different sulfide species appeared. The reflections of MoS2
crystallites are observed at 20 values of 14.6 , 33.4 , 40.9 , and 58.9 in
the XRD
pattern of the alkali-promoted MWCNT-supported, bimetallic Rh-Mo catalyst.48
The peak intensity of the M0S2 crystallites decreased with the addition of Co.
The
peaks at 20 values of 21.5 , 28.4 , 29.9 , and 31.5 are due to the
characteristic
reflections of the K-Mo-S species and are related to active sites for higher
alcohols synthesis.49 The peak at 20 values of 52.4 is due to the different
reflecting planes characteristic of bulk Co9S8 particles.35 The intensity of
these
peaks is high on the activated support, compared to that of MWCNTs.
[00121] The H2-TPR studies (Figure 5) of all the catalysts reveal two
reduction peaks, the low temperature reduction peak is attributed to the
reduction
of bulk MoO3 and the high temperature peak is due to the complete reduction of
MoO2 to lower oxidation state .50,51 The low temperature reduction peak at 385
C,
and the second peak at 760 C were observed in the H2-TPR profile of MWCNT-
supported alkali-promoted bimetallic Rh-Mo catalyst. With the incorporation of
CA 02739142 2011-05-05
29
4.5 wt % Co, the low temperature reduction peak shifted from 385-332 C. The
high temperature reduction feature for the catalyst promoted with 4.5 wt % Co
was observed in the temperature range of 570-740 C, which confirms that the
addition of Co to the alkali-promoted bimetallic Rh-Mo catalyst enhances the
metal species to reduce at low temperatures. The temperature peak attributed
to
the reduction of the octahedral coordinated Mo (Mo6+) species to the
tetrahedral
coordinated Mo (Mo4+) species was further shifted to 305 C, and the reduction
of
the Mo4+ species to a lower oxidation state was observed in the temperature
range of 500-700 C on the MWCNT-supported alkali-promoted trimetallic Co-Rh-
Mo catalyst with 6 wt % Co.
[00122] On the activated carbon-supported catalysts, similar results were
observed, but with the ratio of high to low temperature peaks being greater
than
on the MWCNT-supported catalysts. In addition, some weak features occurred at
higher temperature positions on the activated carbon-supported catalysts,
indicating that more than one kind of oxidic Mo (VI) species existed on the
support. These differences are attributed to the interaction of Mo (or Co)
species
with the activated carbon support.
(b) Higher Alcohols Synthesis
[00123] The catalyst activity studies toward higher alcohol synthesis
reaction were carried out under similar conditions at 320 C, 8.3 MPa (1200
psig),
3.6 m3 (STP)/(kg of cat.)/h, and H2 to CO molar ratio of 1. Figure 6 gives the
results of the percentage CO conversion as time-on-stream during higher
alcohols synthesis reaction over the MWCNT-supported catalyst with 1.5 wt %
Rh, 15 wt % Mo, and 9 wt % K, as well as the trimetallic catalysts promoted
with
varying loadings of Co (4.5 and 6 wt %) supported on MWCNTs and activated
carbon. As Figure 6 shows, during the 24-h alcohol synthesis, CO conversion
was sharply reduced in the first 12 h, and then leveled off, indicating that
the
catalyst was quite stable after 12 h of time-on-stream. A 40% CO conversion
was
observed on the alkali-modified bimetallic Rh-Mo catalyst supported on
CA 02739142 2011-05-05
MWCNTs. The alkali-promoted trimetallic catalysts with 6 wt % Co showed the
highest CO conversion, compared to the catalyst with 4.5 wt % Co, which
confirms that the activity for hydrogenation reaction improved with increased
Co
wt % in the catalyst. The 45 and 49% CO conversions were observed on the
MWCNT-supported 1.5 wt % Rh, 15 wt % Mo, and 9 wt % K catalysts promoted
with 4.5 and 6 wt % Co, respectively. The activated carbon-supported catalysts
promoted with 4.5 and 6 wt % Co showed CO conversions of 31 and 35%,
respectively. The catalytic activity and product selectivity data were
calculated
after an induction period of 15 h.
[00124] The analysis of the liquid products indicates that linear alcohols are
formed and no branched alcohols were observed in the GC trace corresponding
to the higher alcohols. Methanol, ethanol, n-propanol, and n-butanol are the
major products, together with other higher alcohols. The analysis of exit gas
indicates that methane is the major component apart from CO2 and unconverted
gases, such as, CO and H2.
[00125] Table 3 shows the activity and selectivity results obtained from CO
hydrogenation over the sulfided alkali-modified Co-Rh-Mo catalysts. The term
higher alcohols represents the ethanol and alcohols with carbon numbers
greater
than 2 (C2+ alcohols). Over the cobalt-free MWCNT-supported catalyst, the
total
alcohols and total hydrocarbons space time yields (STY) were 0.211 and 0.332
g/(g of cat.)/h, respectively. With the addition of 4.5 wt % Co on the MWCNT-
supported 1.5 wt % Rh, 15 wt % Mo, and 9 wt % K catalyst, the total alcohols
STY increased to 0.244 g/(g of cat.)/h and the total hydrocarbons STY
decreased
to 0.251 g/(g of cat.)/h. The methanol, ethanol, and higher alcohols
selectivities
increased from 5.4%, 16.0%, and 24.6% over the alkali-promoted bimetallic Rh-
Mo/MWCNT catalyst to 6.7%, 20.1%, and 31.4% on the MWCNT-supported
trimetallic catalyst promoted with 4.5 wt % Co. From the CO chemisorption
results, it was observed that incorporation of 4.5 wt % Co to the alkali-
modified
bimetallic Rh-Mo catalyst supported on MWCNTs increased the CO uptake from
CA 02739142 2011-05-05
31
135 to 237 pmole/(g of cat.). Also, Co promotion to Rh-Mo-K/MWCNT catalyst
increased the metal dispersion from 39.5 to 49.8% favoring the formation of
fine
particles. These results, coupled with XRD data, confirm that incorporating Co
metal increased the number of active sites responsible for the formation of
alcohols. The water-gas shift reaction rate decreased significantly with the
addition of Co. By increasing the Co loading from 4.5 to 6 wt % on the MWCNT-
supported trimetallic catalyst, the total alcohols STY decreased from 0.244 to
0.235 g/(g of cat.)/h and total hydrocarbons STY increased from 0.251 to 0.293
g/(g of cat.)/h. With increased Co content from 4.5 to 6 wt %, the CO uptake
increased from 237 to 245 Nmole/(g of cat.), whereas the metal dispersion
decreased from 47.8 to 44.8%. These results confirmed that the methanation
activity of the catalyst is increased with increased Co content from 4.5 to 6
wt %,
because of the formation of large size metal sulfide (Co9S8) sites. On the
MWCNT-supported trimetallic catalyst promoted with 6 wt % Co, the selectivity
of
methanol, ethanol, and higher alcohols decreased to 5.9%, 18.5%, and 27.8%,
respectively.
[00126] The activity and selectivity of the activated carbon catalysts toward
higher alcohols synthesis are comparatively less than that of the catalysts
supported on MWCNTs. This can be explained from the textural properties of the
catalysts. The activated carbon-based catalysts showed a drastic fall in
surface
area and exhibited relatively low pore volume and diameter compared to the
MWCNT-supported catalysts. The pore size of supported catalysts can influence
particle size distribution, dispersion, extent of reduction, and directly
affects mass
transfer diffusion rates of reactants and products. MWCNT supports have the
advantage of large pore volume and pore size that facilitates uniform metal
particle distribution and high dispersions. The activated carbon-supported
catalysts follow similar trends in STY of total alcohols and total
hydrocarbons.
The selectivity of methanol was higher than that of ethanol over the activated
carbon-supported catalysts, confirming that the CO insertion mechanism, which
CA 02739142 2011-05-05
32
promotes the chain growth probability for the formation of higher alcohols
from
methanol, is less effective compared to the catalysts supported on MWCNTs.
[00127] The MWCNT-supported alkali-modified trimetallic catalyst promoted
with 4.5 wt % Co was used to study temperature effects on higher alcohols
synthesis reactions. The reactions were performed under similar conditions at
8.3
MPa (1200 psig) and 3.6 m3 (STP)/(g of cat.)/h. As shown in Figure 7, the CO
conversion and hydrocarbon STY increased monotonically from 36.1 to 51.2%
and 0.218 to 0.292 g/(g of cat.)/h, respectively, with increasing temperature
from
300 to 340 C. The maximum total alcohol STY of 0.261 g/(g of cat.)/h was
observed at 330 C. The methanol selectivity decreased monotonically with
increased temperature, whereas, the ethanol, higher alcohols, and total
alcohols
selectivity displayed a pronounced increase, reaching maxima of 24.5%, 37.3%,
and 42.9% at 330 C (Figure 8).
[00128] To investigate the effects of pressure, the reaction pressures were
varied in the range of 5.5 to 9.7 MPa (800 to 1400 psig) over the MWCNT-
supported, alkali-modified trimetallic catalyst promoted with 4.5 wt % Co at
320 C
and 3.6 m3 (STP)I(g of cat.)/h. Figure 9 shows that increased pressure
monotonically increased the CO conversion, total alcohol formation rate, and
hydrocarbon formation rate. The selectivity of methanol, ethanol, and higher
alcohols also increased monotonically with increasing pressure, indicating
that
increasing pressure at a constant temperature favors the formation of higher
alcohols (Figure 10).
[00129] Table 4 compares the activities of sulfided 4.5 wt % Co, 1.5 wt %
Rh, 15 wt % Mo, and 9 wt % K (catalyst D) supported on MWCNTs with those of
other catalysts discussed in the literature. The catalyst with highest
activity from
each work was selected for comparison purposes. This table indicates that the
sulfided alkali modified Co-Rh-Mo catalysts supported on MWCNTs produces
0.261 g/(g of cat./h) which is much higher than that reported in the
literature.
CA 02739142 2011-05-05
33
Example 2: Alkali and Metal Promoters (Co and Rh) on M0S2 Catalysts for
Higher Alcohols Synthesis: Catalytic Performance and Structural
Characterization Studies
[00130] The role of alkali on the conversion of synthesis gas over MoS2
catalysts to produce higher alcohols is not thoroughly understood. This
example
emphasizes the improved performance of MoS2 catalysts due to the addition of
alkali and metal promoters on modification of surface structure and oxidation
states. This study revealed the formation of Co (Rh)-Mo-S species in the XANES
spectra of bimetallic and trimetallic alkali-promoted MoS2 catalysts, in
agreement
with the improved catalytic performance.
Materials and Methods
(a) Preparation of catalysts
[00131] Commercially available MWCNTs and activated carbon were used
as catalyst supports and the catalysts were prepared by conventional incipient
wetness method, as described in Example 1. Ammonium heptamolybdate
tetrahydrate (AHM), potassium carbonate, cobalt acetate tetrahydrate, and
rhodium chloride hydrate were used as precursors for Mo, K, Co, and Rh,
respectively.
(b) Catalyst studies for higher alcohols synthesis
[00132] The catalytic conversion of synthesis gas to higher alcohols was
performed using the feed gas mixture CO (40 mole %), H2 (50 mole %), and Ar
(10 mole %) in a single-pass tubular downflow fixed-bed reactor under the
reaction conditions of 330 C, 9.1 (1320 psig), and 3.8 m3 (STP)/(kg of cat.)/h
over a period of 24 h. The detailed description about the high pressure
reaction
set up used in this study was discussed in previous papers. 43,52.53,54 Prior
to the
reaction, the catalyst was reduced and sulfided for 6 h at 450 C at a heating
rate of 2 C/min using a gas mixture containing 10 mole % H2S in H2 and a flow
rate of 50 ml/min. The product gas was cooled to 0 C and separated into gas
and
CA 02739142 2011-05-05
34
liquid phases at the reaction pressure. The liquid products were collected at
the
end of the reaction and analyzed with a Varian 3400 gas chromatograph
equipped with a capillary column and a flame ionization detector (FID). The
gaseous products were analyzed online on a Shimadzu gas chromatograph
through a sampling valve for every 1 h. The experiments were repeated at least
twice to check reproducibility and to confirm that the results obtained were
within
the experimental error of 2.5%.
(c) Catalyst characterization
[00133] The surface area, pore volume, and average pore diameter of the
M0S2 catalysts promoted with or without K, Co, and Rh-supported on MWCNT or
activated carbon were measured by N2-physisorption at 77 K using the methods
described in Example 1.
[00134] Powder X-ray diffraction (XRD) analysis patterns of sulfide forms of
samples were recorded on a Rigaku X-ray diffraction instrument as described in
Example 1.
[00135] The S K-edge and Mo L3-edge XANES of the sulfided catalysts
were obtained at the Soft X-ray Microanalysis Beamline (SXRMB) of the
Canadian Light Source (CLS; Saskatoon, SK, Canada) using a Si (111) double
crystal monochromator. CLS, a 2.9 GeV, third generation storage ring,
presently
operates with an injection current of 250 mA. The sample was dispersed on
double-sided conducting carbon tapes under a dry nitrogen atmosphere, and the
measurements were made in both total electron yield by recording the sample
drain current and fluorescence yield using a PGT single element Si(Li) drift
detector. The XANES spectra were normalized to incident photon flux and to
unity at the maximum intensity of each spectrum. Linear combination fitting of
Mo
L3-edge spectra was performed using Athena software. The fitting was performed
using the first derivative curves, and the weights of the components were set
to
be between 0 and 1 and the sum was forced to 1 during the fit.
CA 02739142 2011-05-05
Results and Discussion
(a) Catalyst studies for higher alcohols synthesis
[00136] Figure 11 shows the simplified reaction scheme of higher alcohols
reaction from synthesis gas over alkali-modified MoS2-based catalysts.
According to this CO insertion mechanism,55 CO hydrogenation takes place in
three different steps: (a) chain initiation, (b) chain propagation, and (c)
chain
termination. In the first step, adsorption of CO takes place on the mixed K-Mo-
S
and M-Mo-S phases (M=transition metals such as Co, Ni, Fe, or Rh), while
hydrogen adsorption occurs at the separated metal sulfide sites such as MoSX
and MS, and these surface species react to form R1Os (R1-CH3) intermediates.
These species propagate chain growth through hydrogenation, followed by
insertion of molecularly adsorbed COS to form long chain intermediates R;S (R;
-
CnH2n+1, n = 1, 2, 3, ...) and R;+1% (Ri+1 - C2nH2n+1, n = 1, 2, 3, ...). In
the final
step, direct hydrogenation of these intermediate hydrocarbon species leads to
the formation of alkanes and alkenes, while methanol and higher alcohols are
obtained from hydrogenation of the oxygenated hydrocarbon surface species
(RiOs and R;+1Os). This mechanism results in the formation of linear chain
alcohols due to linear growth by C1 intermediate insertion at the end of the
chain
that is bound to the surface.
[00137] Table 5 shows the activity and selectivity results obtained from the
CO hydrogenation reaction carried out under similar conditions at 330 C, 9.1
MPa (1320 psig), 3.8 m3 (STP)/(kg of cat.)/h, and H2 to CO molar ratio of 1.25
over the sulfided Mo- based catalysts promoted with or without K, Co, and/or
Rh.
The analysis of the liquid products indicates that linear alcohols are formed
and
no branched alcohols were observed in the GC trace corresponding to the higher
alcohols. The term higher alcohols represents ethanol and alcohols with a
carbon
number greater than 2 (C2+ alcohols). Methanol, ethanol, n-propanol, and n-
butanol are the major liquid products, together with other higher alcohols.
The
CA 02739142 2011-05-05
36
analysis of exit gas indicates that methane is the major component, apart from
CO2 and unconverted gases such as CO and H2.
[00138] The % CO conversion increased with the addition of metal
promoters, Co and Rh over the sulfided Mo-K/MWCNTs catalyst. Among the
alkali-promoted MWCNTs catalysts, the trimetallic Co-Rh-Mo catalyst showed
the highest CO conversion of 51.2%, confirming that CO hydrogenation is
improved with the addition of metal promoters to the alkali-modified MOS2
catalysts. Improved CO hydrogenation (% CO conversion 64.8%) is observed
over the MWCNT-supported trimetallic catalyst without K. A lower CO conversion
of 35.6% was observed on the alkali-promoted trimetallic catalyst supported on
activated carbon, indicating that the CO hydrogenation activity was
comparatively
higher on catalysts supported on MWCNTs. The lower performance of activated
carbon supported catalysts can be explained due to the microporous nature of
the support, resulting lower dispersions of metal species.54
[00139] The total alcohols and total hydrocarbons space time yields (STY)
of 0.12 and 0.19 g/(g of cat./h), respectively, were observed over the
sulfided Mo-
K/MWCNTs catalyst. The addition of Co and Rh to the Mo-K/MWCNTs catalyst in
sulfided form increased the total alcohols STY to 0.26 and 0.26 g/(g of
cat.)/h,
respectively, and the total hydrocarbons STY to 0.39 and 0.36 g/(g of cat.)/h,
respectively.
[00140] The alkali-promoted trimetallic Co-Rh-Mo catalyst supported on
MWCNTs showed an improved total alcohol STY of 0.29 g/(g of cat.)/h, whereas
the total hydrocarbon STY decreased, compared to that of alkali-promoted
bimetallic catalysts. The decreased methanol selectivities and increased
selectivities of ethanol and higher alcohols were observed on the bimetallic
alkali-
promoted catalysts supported on MWCNTs compared to that of monometallic
catalyst. The highest ethanol and higher alcohols selectivities of 25.7 and
39.4%
are observed on the trimetallic catalyst promoted with alkali and supported on
MWCNTs.
CA 02739142 2011-05-05
37
[00141] The alkali-promoted trimetallic catalyst supported on activated
carbon showed a total alcohols and total hydrocarbons STY of 0.19 and 0.22
g/(g
of cat.)/h, respectively. The alkali-promoted trimetallic catalyst supported
on
activated carbon showed the highest selectivity towards methanol, compared to
that of ethanol and other higher alcohols. This confirms that the chain growth
mechanism that promotes the formation of higher alcohols is less effective on
activated carbon supported catalysts compared to the catalysts with MWCNTs
support.
(b) Catalyst characterization
Textural characteristics
[00142] The textural characteristics of all the catalysts are shown in Table
6.
The surface area and pore volume of all the catalysts were decreased compared
with
that of the support due to the pore blocking and surface smoothing by the
deposition
of metals in sulfide state on the support. The BET surface area of Mo-K/MWCNT
catalyst was found to be 109 m2/g. With the incorporation of Co and Rh to the
Mo-
K/MWCNT catalyst, the surface area was decreased to 89 and 86 m2/g,
respectively. The alkali-promoted trimetallic Co-Rh-Mo/MWCNT catalyst showed a
BET surface area of 79 m2/g, whereas the trimetallic catalyst not promoted
with K
showed a BET surface of 68 m2/g. These results suggest that alkali helped to
disperse the metal species on the support, favouring the formation of small
particles.
A drastic fall in surface area over the activated carbon-supported catalysts
was
observed.
[00143] Activated carbon is a microporous support and has relatively low pore
volume and pore size compared to that of MWCNTs, which are mesoporous in
nature. The particle size distribution, dispersion, and extent of reduction
depend on
the pore size of supported catalysts and directly affect mass transfer
diffusion rates of
reactants and products. MWCNT supports have the advantage of large pore volume
CA 02739142 2011-05-05
38
and pore size, which facilitate uniform metal particle distribution and high
dispersions
products.56
(c) X-ray diffraction
[00144] The XRD patterns of the catalysts in sulfided form were measured
and are shown in Figure 12. The JCPDS chemical spectra data bank was used
to detect the most probable phases present in the samples, and the results of
the
possible crystal phases with their corresponding reflection planes are given
in
Table 7. The intense peaks at d-spacing of 3.35 are due to the reflections of
the
graphite phase present in the MWCNT and activated carbon supports. 57 The
reflections of MoS2 crystallites are observed at d-spacing values of 6.11,
2.71, and
1.57 (Figure 12 (a)). 58 With the addition of metal promoters, Co and Rh, new
peaks, such as at d-spacing of 3.02 and 1.75, can be observed, suggesting the
formation of the new phases, Co (Rh)-Mo-S. These new phases are related to
the electron donation from Co (Rh) to Mo. The formation of Co (Rh)-Mo-S
decreases the Mo-S bond strength to an optimum range and significantly
increases the activity of the catalyst towards the formation of higher
alcohols.
[00145] The peaks at d-spacing of 3.1, 3.02, and 2.78 are observed on all
the catalysts promoted with K. These are due to the characteristic reflections
of
the K-Mo-S species, and are related to active sites for higher alcohols
synthesis.59 The peak at d-spacing of 1.75 is due to the different reflecting
planes
characteristic of bulk Co9S8 particles.60 The XRD patterns of the Co-Rh-Mo
trimetallic catalyst without the alkali promoter mainly revealed three peaks
due to
the characteristic reflections of graphite carbon, M0S2, and C09S8 species.
The
intensity of these crystalline peaks is found to be large compared to the
alkali-
promoted catalyst, suggesting that alkali reduces the crystalline nature of
the
catalyst particles and favours the formation of smaller particles.
(d) XANES: Overview
CA 02739142 2011-05-05
39
[00146] Figure 13 shows the S K-edge and Mo L3-edge XANES spectra of
MoS2 and three trimetallic MoS2 catalysts. The total electron yield (TEY) is
more
surface sensitive, with an estimated probing depth of 100 nm at the S K-edge
(Figure 13(a)); while the fluorescence yield (FLY) is more bulk sensitive,
with a
probing depth about 10 times deeper than that of TEY (Figure 13(b)). The TEY
and
FLY spectra for these samples are essentially identical in peak energy
positions, but
quite different in relative peak intensities. These spectra can be divided
into three
general regions: region A, around 2471 eV, is due to the S 1s to 3p dominated
transitions of S in -2 oxidation state, such as MoS2; region B appearing at
2481 eV is
associated with the presence of oxidized sulfate (S04 2) species; and region C
around 2524 eV is assigned to absorptions as a result of transitions from Mo
2p3/2
initial state to empty orbitals with mainly Mo 4d characters. Compared to the
sulfide
peak (A), the relative intensities of peaks B and C are higher in the TEY
spectra,
indicating a more oxidized surface (Figure 13(a) vs Figure 13(b)). It is worth
noting
that the sulfate peak (B) is more pronounced in the K-promoted trimetallic
systems,
while there is little or no sulfate observed in spectra of the MoS2 and of the
catalyst
without K. This is consistent with the XRD observation that only diffraction
patterns
due to MOS2 and Co9S8 are present in the trimetallic catalyst without the
alkali
promoter (Figure 12). The formation of sulfate species in the K-promoted MoS2
catalysts is due to the oxidation of sulfur in the presence of oxygen of the
molybdates.61
[00147] Zubavichus et al.62 explained that the oxidation of MoS2 takes place
at surface-situated active centers located in the non-intercalated amorphous
outer region of the particles. This partial oxidation of the sample is in
agreement
with the previous observation of S oxidation during synthesis and/or ageing by
Guay et al.63 S oxidation with Mo atom is also evident in the Mo L3-edge
results,
as a shoulder peak at 2527.7 eV, due to the oxidized Mo, can be observed in
the
spectra of K-promoted catalysts. The alkali promotion leads to the formation
of
new phases, such as K-Mo-S, thus decreasing the number of available Mo sites.
CA 02739142 2011-05-05
These results indicate that alkali promotion increased the susceptibility of
M0S2
layers to oxidation, thus improving the catalytic performance for higher
alcohols
yield. On the other hand, the trimetallic system without K promotion has very
high
(little) hydrocarbon (alcohol) conversion yield (Table 5). Its S K-edge
spectrum is
similar to that of M0S2, confirming the importance of role of oxidation of
MoS2 in
production of high alcohols. The peak intensities of sulfide and Mo of the
catalyst
supported on MWCNTs are found to be higher than those of the activated carbon,
consistent with the higher catalytic performance observed for catalysts
supported
on MWCNTs (Table 5).
(e) XANES: the S K-edge
[00148] The S K-edge XANES spectra of sulfur standards (MoS2 and
FeSO4) and the MWCNT-supported alkali-promoted MoS2 catalysts promoted
with or without Co and Rh recorded in TEY are displayed in Figure 14. Compared
to the spectra of sulfur standards, it is clear that both sulfide and sulfate
species
are present in all alkali-promoted catalysts. The broadening of peak A for
alkali-
modified MoS2-based catalysts, in particular the additional shoulder in peak A
of
the Co-Rh-Mo-K/MWCNT sample, providing further evidence of the formation of
Co (Rh)-Mo-S networks in the Co and Rh-promoted catalysts. Peak B of the
alkali-promoted catalysts is broader with additional intensity at the lower
energy
side, compared to that of FeSO4. This is likely due to the formation of
sulfate of a
mixed nature (K-Mo-S, Co-Mo-S or Rh-Mo-S) in bimetallic and trimetallic
catalysts and the chemical shift is due to stronger bonding between Fe and
sulfate over the bonding between Mo (and/or Co, Rh) and sulfate. Finally, an
additional shoulder around 2477 eV (peak B) can be observed in the spectra of
alkali-promoted catalysts, a feature usually associated with intermediate
sulfur
species with an oxidation state of +4 or +2 64 These results indicate that the
formation of new phases (K-Mo-S, Co-Mo-S, and/or Rh-Mo-S) takes place with
the addition of promoters, decreasing the crystalline nature of MoS2 species,
which correlates well with the catalytic performance shown in Table 5.
CA 02739142 2011-05-05
41
(fJ XANES: Mo L3 - edge
[00149] The Mo L3-edge XANES of reference compounds, MoS2 (Mo
oxidation state +4) and ammonium hepta molybdate (AHM) (Mo oxidation state
+6), and the MWCNT-supported alkali-promoted MoS2 catalysts, recorded in TEY-
mode spectra are given in Figure 15. The Mo L3-edge of MoS2 was observed at
2523.6 eV with a shoulder peak at 2530.7 eV due to the tetrahedral
coordination of
Mo atoms.65 The Mo L3-edge XANES spectrum of ammonium hepta molybdate
(AHM) displayed a characteristic doublet at 2525.0 and 2527.5 eV, as a result
of the
ligand field splitting of the d final states under octahedral symmetry.63 The
Mo L3-
edge spectra of the MWCNT-supported alkali-promoted bimetallic or trimetallic
catalysts shown in Figure 15 are somewhat different from those of the Mo model
compounds. The main peak is at a very similar energy position (2524.0 eV) to
that
of MoS2, suggesting that presence of MoS2 in these catalysts. The broadening
of the
main peak and the presence of the second peak at 2527.7 eV that overlaps the
doublet of the AHM spectrum, strongly suggest the oxidation of Mo in these
catalysts with the addition of Co and Rh. The intensity of 2527.5 eV peak
follows the
order of Co-Rh-Mo-K/MWCNT > Co-Mo-/MWCNT>RH-Mo-K/MWCNT>Mo-
K/MWCNT.
[00150] Figure 16 presents the linear combination fitting of the Mo L3-edge
spectra of the catalyst Mo-K/MWCNTs. Spectra of MoS2 and AHM are used as
standards in the fitting. Based on the fitting, the oxidized Mo+6 species is
estimated to be 19.2%, 11.5%, and 0.4% for the Mo-K/MWCNT, Co-Rh-Mo-
K/MWCNT, and Co-Rh-Mo/MWCNT catalysts, respectively. In trimetallic
catalysts without K, the Mo species mainly exist as MoS2 state, whereas the
addition of K favours the oxidation of Mo+4 to Mo+6 states. The addition of
transition metal promoters (Co and Rh) to the Mo-K catalyst leads to the
formation of Co-Mo-S phase, in which Mo exits mainly in +5 oxidation state,
which is the active phase for the formation of higher alcohols. The decreased
66
CA 02739142 2011-05-05
42
amount of Mo+6 species due to the promotion of Co and Rh to the Mo-K catalyst
suggests the reduction of Mo from +6 to +5 oxidation state.
[00151] The trimetallic catalyst without K showed improved activity towards
the
formation of hydrocarbons and very little activity for the alcohols synthesis
reaction.
From the results of XRD and XANES, it was observed that the intensity of the
metal
sulfide peaks is large (no sulfate intensity) and the BET surface area is less
on the
trimetallic catalyst that is not promoted with K, compared to that of alkali-
promoted
trimetallic catalyst. The results in the present study implied that the
addition of K is
beneficial to the dispersion of large metal sulfide agglomerates to small
particles on
the support by favouring the formation of chemically combined new phases (Co
(Rh)-
Mo-S) in sulfide state. This suggests that the promotion of alkali reduces the
hydrogenation ability of alkyl species to form alkanes and increases the
active sites
for the formation of alcohols.
(g) Conclusions
[00152] The addition of Co and Rh, to the sulfided Mo-K/MWCNT catalyst
improved the space time yield and selectivity of the higher alcohols. The
maximum total alcohols yield of 0.29 (g/(g of cat./h)) and higher alcohols
selectivity of 39.4% were obtained over the Co-Rh-Mo-K/MWCNT catalyst at
330 C, 1320 psig (9.1 Mpa), 3.8 m3 (STP)/(kg of cat.)/h using H2 to CO molar
ratio value of 1.25. The AC-supported Co-Rh-Mo-K catalyst had a much higher
hydrocarbon formation, while the MWCNT-supported alkali-promoted trimetallic
catalyst showed better alcohols yield. Alkali promotion to the M0S2 catalyst
reduced
the crystalline nature of the catalyst and favored the formation of alcohols.
More
oxidized S and Mo species were also observed by XRD and XANES in the K-
promoted catalysts, indicating the formation of more Mo oxide and/or Co oxide
with
the addition of K, thus increasing the active sites. More intense features
corresponding to the oxidized S and Mo species were observed in both S K-edge
and
Mo L3-edge spectra of the MWCNT-supported catalysts. The formation of Co (Rh)-
CA 02739142 2011-05-05
43
Mo-S species was evident in the XANES spectra of the bimetallic and
trimetallic alkali-
promoted MoS2 catalysts, in agreement with their improved catalytic
performance.
Example 3: Influence of Porous Characteristics of the Carbon Support on
Alkali-Modified Trimetallic Co-Rh-Mo Sulfided Catalysts
Materials and Methods
(a) Catalyst preparation
[00153] Four catalysts listed in Table 8 were prepared using different
activated carbons. AC-Darco, brand named activated carbon was purchased
from Aldrich, Canada. Two activated carbons, brand named as AC-RX3 extra and
AC-CGP super were obtained form Norit, USA. Activated carbon named as AC-
Fluid coke is obtained from Syncrude and activated in our pilot scale reactor.
Commercial MWCNTs were purchased from M. K. Nano, Canada. Prior to
impregnation, all the supports were treated with 30% HNO3 reflux at 100 C
overnight, washed with distilled water several times, and dried at 120 C for 6
h.
The oxide samples were prepared by the incipient wetness impregnation method
using ammonium heptamolybdate tetrahydrate (Sigma-Aldrich, Canada),
potassium carbonate (Aldrich, Canada), cobalt acetate tetrahydrate (Alfa-
Aesar,
Germany), and rhodium chloride hydrate (Aldrich, Canada) as precursors for Mo,
K, Co, and Rh, respectively. At the first step, the support was impregnated
with
an aqueous solution of K2CO3, followed by drying at 120 C for 2 h and
stabilizing
in an argon flow of 50 ml/min at 300 C, at a heating rate of 10 C/min for 4 h.
The
support was further impregnated with aqueous solutions containing the required
amounts of (NH4)6Mo7O24, Co(CH3COO)2, and RhCl3 followed by drying at 120 C
for 2 h and stabilizing in an argon flow of 50 ml/min at 450 C, at a heating
rate of
C/min for 12 h.
(b) Characterization of Co-Rh-Mo-K catalysts
CA 02739142 2011-05-05
44
[00154] The surface area, pore volume, and average pore diameter of oxide
samples were measured by N2-physisorption at 77 K using the method described
in Example 1.
[00155] The content of Mo, Co, and Rh of the oxide catalysts was
determined as described in Example 1.
[00156] Powder X-ray diffraction (XRD) analysis patterns of oxide forms of
samples were recorded on a Rigaku X-ray diffraction instrument as described in
Example 1.
[00157] Carbon monoxide was used as a probe molecule to determine the
number of accessible surface metal atoms present on the sulfided catalysts as
described in Example 1.
[00158] The morphology of the oxide samples was characterized by
transmission electron microscopy (TEM) investigations as described in Example
1.
(c) Catalyst activity and selectivity studies
[00159] A single-pass tubular downflow fixed-bed reactor of 450-mm length
and 22-mm inside diameter made of inconel tube was used to perform higher
alcohol synthesis reactions. The reactor was packed with 2 g of catalyst
diluted
with 12 ml of 90 mesh size silicon carbide and housed in an electric furnace
controlled by a temperature controller. The reactor was pressurized with He to
3.44 MPa (500 psig) and the sulfidation, together with the reduction, was
carried
out for 6 h at 450 C at a heating rate of 2 C/min using a gas mixture
containing
mole % H2S in H2 and a flow rate of 50 ml/min. The temperature was then
lowered to the reaction temperature, and the system pressurized to the
reaction
conditions. The feed gas mixture CO (30 mole %), H2 (60 mole %), and Ar (10
mole %) was passed through mass flow controllers and the higher alcohols
synthesis reaction was carried out at steady-state under the reaction
conditions
of 330 C, 8.27 (1200 psig) and a gas hourly space velocity (GHSV) of 3.6 m3
CA 02739142 2011-05-05
(STP) /(kg of cat.)/h over a period of 24 h. The product gas was cooled to 0 C
and separated into gas and liquid phases at the reaction pressure. The CO
conversion and other gaseous products were monitored with a time interval of 1
h. The liquid products were collected at the end of the reaction and analyzed
with
a Varian 3400 gas chromatograph equipped with a capillary column and a flame
ionization detector (FID). The volume and weight of liquid products were
measured to check the mass balance. The gaseous products were analyzed
online on a Shimadzu gas chromatograph through a sampling valve. Using Ar as
an internal standard, the CO conversion was calculated and the overall mass
balance of the reaction was determined. The experiments were repeated at least
twice to check reproducibility and to confirm that the results obtained were
within
the experimental error of 2.5%.
Results and Discussion
(a) Characterization of Co-Rh-Mo-K catalysts
[00160] The N2 adsorption-desorption isotherm of all the supports were
measured with an aim to measure the total surface area and are shown in
Figures 17a to 17e. The microporous activated carbon support, AC-Darco,
exhibits a type III isotherm with a hysteresis loop of type H2 according to
the
IUPAC classification.67 Type 11 adsorption isotherm with a hysteresis loop of
type
H2 is observed on the support, AC-Rx3 extra.68 A horizontal plateau at
relative
higher pressures indicates highly microporous nature of this support with a
narrow pore size distribution. On the support, AC-Fluid coke, the increment of
N2
uptake was significant at high relative pressures and showed type IV isotherm
with a hysteresis loop of type H3 that does not exhibit any limiting
adsorbtion at
high relative pressures.67 This indicates the presence of large amount of
mesopores on this support. The N2 adsorption-desorption characteristic type IV
isotherm with large condensation of adsorbate in pores at mesoporous regions
(x
67
p/ps 2: 0.40) was observed on the mesoporous support, AC-CGP super. The
=
CA 02739142 2011-05-05
46
MWCNT support showed the characteristic type IV isotherm with H1 hysteresis
loop, indicative of the existence of textural mesopores with cylindrical
arrays of
pore channels. The sharpness of the desorption branches suggests the narrow
pore size distribution of the MWCNT support .69 Figure 18a to 18e displays the
N2
adsorption-desorption isotherms of all the catalysts. From these figures, it
is cleat
that the amount of N2 adsorbed on the support is proportional to the available
surface area. All the catalysts exhibit similar isotherms as their
corresponding
supports, suggesting that metal impregnation did not alter the structure of
the
parent support.
[00161] The results for textural characterization of supports as well as the
catalysts are summarized in Table 8. Data are tabulated for BET surface area
(SBET), mesopore surface area (Sme), total pore volume (Vtot), mesoporous
volume (Vme), average pore diameter (D), and the percentage of mesoporosity
(% Me), defined as percentage ratio of mesopore due to metal loading was
calculated using BE = 1- NSBET, where NSBET is the normalized surface area,
and is defined as NSBET = (SBET)cataiyst/((1- Y) * (SBET)support), in which y
is the
weight fraction of the total metal content of the catalyst.70 It is observed
from the
table that the support, AC-Fluid coke has low surface area and pore volume
among the activated carbon supports. The support, AC-CGP super displays the
highest BET surface area, total pore volume and mesoporous volume. MWCNTs
exhibit low surface area compared to that of activated carbon supports,
whereas,
the pore diameter is found to be quite high. The supports AC-CGP super and
MWCNTs are highly mesoporous in nature with mesoporosity of 94 and 98%,
respectively.
[00162] The textural properties of the stabilized catalysts display some
changes to that of pure supports. The mean pore diameter and % mesoposity
were shifted towards higher values after the impregnation of alkali and metals
on
the supports. These results suggest that the addition of metals most likely
block
CA 02739142 2011-05-05
47
the micropores of the support .71 The BET surface area and pore volume
decrease were observed after the incorporation of metals, suggesting the
partial
pore blocking of the support by the metals. The blocking extent of the metal
species was found to be high on the microporous activated carbon supported
catalysts. The large surface area of the AC-CGP super supported catalyst
indicates negligible blocking of pores with the impregnated metals. The
decreased mesopore volume and surface area of AC-CGP super-supported
catalyst indicated that the metal species block the mesopore pores of this
support. In spite of the pore blockage, the mesoporous structural integrity of
the
MWCNT-supported alkali-promoted trimetallic C-Rh-Mo catalyst was unchanged
from the support as seen from the N2 adsorption-desorption isotherms of
MWCNT support and the catalyst (Figure 18e). These results suggest that
MWCNTs have unique characteristics, such as uniform pore-size distribution,
nano-sized channels, and mesoporous nature which make them a promising
support for various catalytic applications.
[00163] Figure 19 shows the XRD patterns of the alkali-promoted trimetallic
Co-Rh-Mo catalysts supported on various activated carbons and that of the
MWCNTs in oxide form. The JCPDS chemical spectra data bank was used to
detect the most probable phases present in the samples. The variation in peak
intensity of the catalysts was observed, confirming the role of the support on
the
dispersion of catalyst species. The strong intensity peak at 20 value of 26.6
for the
catalyst supported on MWCNTs is due to the reflections of the graphite phase.
It is
of interest to note that the graphite nature of the support was observed on
micro
porous activated carbons, AC-Darco and AC-RX3 extra, whereas, the XRD
patterns of the catalysts supported on mesoporous activated carbons, AC-
Fluid Coke and AC-CGP super showed no graphite phase. The characteristic
reflections corresponding to the crystalline structure of MoO3 are observed at
20
value of 40.7 on all the catalysts. The peak at 28 value of 28.4 corresponds
to the
72
CA 02739142 2011-05-05
48
characteristic reflections of the K2Mo2O7 phase.73 Other K-Mo-O phases, such
as
KMo4O6 (26 = 15.9, and 37.1 ) also exist on these catalysts. 74,75
[00164] TEM images of the AC-Darco, AC-RX3 extra, AC-Fluid coke, AC-CGP
super and MWCNT-supported catalysts were recorded and are as shown in Figure
20. These micrographs reveal the morphology differences of alkali-promoted
trimetallic Co-Rh-Mo catalysts supported on different supports and the
development
of a considerable amount of agglomerates, especially on the surface of the
microporous activated carbon supported catalysts. The metal species are well
dispersed on the mesoporous activated carbon support, AC-CGP super with
particle
size in the range of 3-6 nm (Figure 20d). The TEM image of MWCNT-supported
catalyst revealed that the catalyst particles are well dispersed both inside
and outside
the carbon nanotubes. The particle sizes of the metal species that are inside
and
outside of the tubes are in the range of 1 to 3 nm (Figure 20e).
[00165] The results of the CO chemisorption of the sulfided catalysts are
given
in Table 9. The CO uptake values of 137 and 140 pmole/(g of cat.) were
observed
on the alkali promoted trimetallic catalysts supported on microporous
activated
carbon supports, AC-Darco and AC-RX3 extra, respectively. Even though the
surface area of the AC-RX3 extra support is almost double, the pore volume and
pore
diameter are comparatively less than that of AC-Darco and hence about equal
amounts of CO chemisorption was observed on these two supports. From the TEM
images, it is observed that the formation of large particles takes place due
to the
agglomeration of metal species on the microporous activated carbon supports.
This
result in lower dispersions on these supports compared to that on mesoporous
activated carbons. Due to the mesoporous nature of activated carbon supports,
AC-
Fluid coke and AC-CGP super, most of the metal deposition takes place inside
the
pores, resulting higher CO uptake values on these supports. The amounts of
adsorbed CO on the surface of MWCNT-supported catalyst is found to be higher
compared to all activated carbon supported catalysts, indicating the presence
of
large number of active sites on the catalyst. The metal dispersion of
catalysts on
CA 02739142 2011-05-05
49
different supports is in the following order: MWCNTs < AC-CGP super < AC-Fluid
coke < AC-RX3 extra < AC-Darco. The large pore volume and pore size of the
MWCNT support facilitates uniform metal particle distribution and high metal
dispersions. These results suggest that the catalyst supported on MWCNTs may
perform better than catalysts supported on microporous, as well as, mesoporous
activated carbons.
(b) Catalyst activity and selectivity studies
[00166] The catalyst activity studies towards higher alcohol synthesis
reaction
were carried out under similar conditions at 330 C, 8.3 MPa (1200 psig), 3.6
m3
(STP)/(kg of cat.)/h, and H2 to CO molar ratio of 2. Figure 21 gives the
results of the
percentage CO conversion as time-on-stream during 24 h of higher alcohol
synthesis
over the different activated carbon and MWCNT-supported alkali modified
trimetallic
Co-Rh-Mo catalysts. It is observed that the CO hydrogenation activity of the
supported catalysts followed the same order as that of CO chemisorption
according
to their pore structures. The stability of MWCNT-supported catalyst was much
better
than the catalysts supported on activated carbons. The uniform pore size
distribution
of the MWCNT support facilitates the large dispersion of metal particles on
the
support, which results in higher activity compared to that on activated carbon
supported catalysts. The catalyst supported on AC-CGP Super showed high
initial
activity at the start-of-run, but dropped sharply as the reaction progressed
within 24 h
period. Similar stability results were observed on the AC-Fluid Coke supported
catalyst. It can be deduced that the partially blocked mesopores by metal
species
raised the mass diffusion restriction of synthesis gas as well as products,
thus
decreasing the CO hydrogenation activity with time-on-stream. The analysis of
the
liquid products indicates that linear alcohols are formed and no branched
alcohols
were observed in the GC trace corresponding to the higher alcohols. Methanol,
ethanol, n-propanol, and n-butanol are the major products, together with other
higher alcohols. The analysis of exit gas indicates that methane is the major
component apart from CO2 and unconverted gases, such as, CO and H2. Table 10
CA 02739142 2011-05-05
shows the activity and selectivity results obtained from CO hydrogenation over
the
sulfided alkali-promoted trimetallic Co-Rh-Mo catalysts after an induction
period of
15 h. The term higher alcohols represents the ethanol and alcohols with carbon
number greater than 2 (C2+ alcohols). Over the catalysts supported on
microporous
activated carbons, AC-Darco and AC-RX3 extra, the total alcohols space time
yields
(STY) of 0.141 and 0.154 g/(g of cat./h), respectively, were observed.
Catalysts
prepared on mesoporous activated carbon, AC-Fluid coke and AC-CGP super had
substantially higher STY of alcohols of 0.187 and 0.202 g/(g of cat./h),
respectively
than microporous activated carbon supported catalysts. The support AC-CGP
super
has the advantage of high surface area, large pore diameter and pore volume
compared to the other activated carbon supports. This results in high
dispersion of
active metal species on the surface as seen from the XRD profiles and CO
chemisorption results, favouring the formation of alcohols. The STY of total
hydrocarbons follow the similar trend as that of the total alcohols STY,
whereas, the
water-gas-shift reaction rate is almost constant on all activated carbon
supported
catalysts. It is also noted that the selectivity of methanol, ethanol and
higher alcohols
are almost constant on all the activated carbon-supported catalysts.
[00167] MWCNT-supported catalysts outperformed the catalysts supported on
activated carbon. The total alcohols and total hydrocarbons STY of 0.296 and
0.345
g/(g of cat./h) were observed on this catalyst, whereas, the carbon dioxide
formation
rate is less compared to that of the activated carbon supported catalysts.
These
results explain that the pore size of the support has direct influence on the
synthesis
of mixed alcohols from synthesis gas. Support pore size can influence particle
size
distribution, dispersion, extent of reduction and plays an important role to
diffuse the
reactant molecules to the catalytically active centers that are located inside
the
pores. The micro-porous structure of activated carbon-supported catalysts
causes
pore plugging due to the formation of coke and deactivation of the catalyst,
which
results in transport limitation in the reaction. It is also worth to note that
all these
activated carbons are associated with 5-10% ash content as indicated by the
CA 02739142 2011-05-05
51
manufacturer, whereas, the MWCNTs are highly purified and has almost
negligible
ash content.
Example 4: Higher Alcohols Synthesis from Synthesis Gas over Sulfided
Alkali-Promoted Co-Rh-Mo Trimetallic Catalyst: Experimental and Modeling
Studies
Materials and Methods
(a) Catalyst preparation
[00168] Catalysts were prepared as described in Example 1.
(b) Catalytic studies
[00169] The higher alcohols synthesis reaction from synthesis gas was
studied using a single-pass tubular downflow fixed-bed reactor of 450-mm
length
and 22-mm inside diameter made of inconel tube. The reactor was packed with 2
g of catalyst diluted with 12 ml of 90 mesh size silicon carbide and housed in
an
electric furnace controlled by a temperature controller. The reactor was
pressurized with He to 500 psig (3.44 MPa) and sulfidation, together with
reduction, were carried out for 6 h at 450 C at a heating rate of 2 C/min
using a
gas mixture containing 10 mole % H2S in H2 and a flow rate of 50 ml/min. The
temperature was then lowered to the reaction temperature, and the system
pressurized to the reaction conditions. The feed gas mixture (desired molar
ratio
of CO and H2 mixed with 10 mole % Ar) was passed through mass flow
controllers and the higher alcohols synthesis was carried out at steady-state
under the reaction conditions over a period of 24 h. The product gas was
cooled
to 0 C and separated into gas and liquid phases at the reaction pressure. The
CO conversion and other gaseous products were monitored with a time interval
of 1 h. The liquid products were collected at the end of the reaction and
analyzed
with a Varian 3400 gas chromatograph equipped with a capillary column and a
flame ionization detector. The volume and weight of liquid products were
measured to check the mass balance. The gaseous products were analyzed
CA 02739142 2011-05-05
52
online on a Shimadzu gas chromatograph through a sampling valve. Using Ar as
an internal standard, the CO conversion was calculated and the overall mass
balance of the reaction was determined.
(c) Experimental Design
[00170] The parameters T, P, and GHSV were varied in the ranges of 275
to 350 C, 800 to 1400 psig (5.52-9.65 Mpa), and 2.4 to 4.2 m3 (STP)/(kg of
cat.)/h, respectively. To analyze the interaction effects between the
operating
parameters for higher alcohols synthesis and to optimize the effective
parameters, the Taguchi orthogonal array design method was used to develop
the experimental plan. This statistical design approach minimizes the overall
variance of the estimated parameters and reduces the number of trials required
without restricting the confidence region for the estimated parameter. 76 An
orthogonal array selector determines the number of trials necessary and the
factor levels for each parameter in each trial." The experiments were designed
using Design-Expert software version 6Ø1, and were performed using a feed
gas mixture of 45 mole % CO, 45 mole % H2, and 10 mole % Ar. Specific
experimental conditions were repeated several times to observe the
reproducibility of the results. A separate set of experiments were performed
to
study the effect of the H2 to CO molar ratio on higher alcohols synthesis at
the
optimum conditions of T, P, and GHSV.
[00171] The perturbation plots were used in conjunction with the 3-D
surface responses, as interpreting the 3-D surface response alone can be
difficult.27 Perturbation plots were used to show the effect of each
individual
variable as the others were held constant. This plot is a powerful method of
comparing the relative influences of factors, and can be used to look at one-
dimensional paths through a multifactor surface.
Results and Discussion
CA 02739142 2011-05-05
53
[00172] Analysis of the liquid products indicates that the alcohols likely
followed the CO insertion mechanism; forming linear alcohols.55 Methanol,
ethanol, n-propanol, and n-butanol are the major products, together with other
higher alcohols. The term higher alcohols represent alcohols with a carbon
number greater than 1, whereas, total alcohols represent methanol and higher
alcohols combined. The analysis of exit gas indicates that methane is the
major
hydrocarbon component apart from CO2, unconverted CO, and H2.
(a) Effects of the temperature, pressure, and gas hourly space velocity
on % CO conversion
[00173] Figures 22a and 22b are three-dimensional (3-D) plots of the
effects of T, P, and GHSV on % CO conversion. The plots show that inlet % CO
conversion increased monotonically with increasing reaction temperature and
pressure from 275 to 350 C and 800 to 1400 psig, respectively. This confirms
that the hydrogentaion of CO over the MWCNTs-supported alkali-promoted
trimetallic Co-Rh-Mo catalyst was greatly improved at high temperature and
pressure. With increased GHSV from 2.4 to 4.2 m3 (STP)/(kg of cat.)/h, it was
observed that the % CO conversion decreased monotonically.
[00174] Short contact time between the reactants at high GHSV resulted in
the low CO conversion. Figure 22c is the perturbation plot showing that the
effects of the variables T, P, and GHSV are significant on % CO conversion.
Figure 22d compares the experimental values to the predicted % CO conversion,
and clearly shows that the model for % CO conversion is valid within the
experimental ranges.
(b) Effects of the temperature, pressure, and gas hourly space velocity on
STY of alcohols, hydrocarbons, and CO2
[00175] Figures 23a and 23b (3-D response surface) and Figure 23c
(perturbation plot) depict the effects of T, P, and GHSV on STY of methanol
using H2 to CO molar ratio equal to 1. The methanol STY decreased
CA 02739142 2011-05-05
54
monotonically with increasing temperature, suggesting that conversion of
methanol to higher alcohols takes place at high temperatures. The formation of
methanol increased monotonically with increasing pressure and GHSV. At high
GHSVs, the consumption of methanol to higher alcohols is low, which explains
the high methanol yields. Table 11 shows the R2 value of 0.993 obtained from
the
fitness of the experimental methanol STY values with that of the predicted
values, confirms that the model fits well within the experimental conditions.
[00176] The effects of T, P, and GHSV reactions on the STY of ethanol at
H2 to CO molar ratio of 1 are represented as 3-D plots in Figures 24a and 24b
and the perturbation plot in Figure 24c. Compared to P and GHSV, temperature
had great effect on ethanol STY, with the rate of ethanol formation reaching a
maximum value and then decreasing at higher temperatures. Depending on the
temperature, the ethanol formation increased upto certain pressures and then
remained constant. With respect to GHSV, a maxima in the ethanol STY was
also observed. The model fits the experimental results with an R2 value of
0.981
as seen from Table 11. Higher alcohols STY exhibit similar trends of operating
conditions dependency as that of ethanol STY, with the maximum amount of
higher alcohols formation observed with respect to temperature and GHSV. With
increased pressure, the higher alcohols STY increased to a certain value and
then remained constant at higher pressures. The fit of the model is good with
an
R2 value of 0.980 (Table 11).
[00177] The dependence of total alcohol formation on the T, P, and GHSV
reactions at H2 to CO molar ratio of 1 are presented as 3-D plots in Figures
25a
and 25b and the perturbation plot in Figure 25c. Table 10 displays the quality
of
the model's fit with an R2 value of 0.982. The total alcohols STY exhibits the
maximum with respect to reaction temperature. Increased pressure favors the
formation of total alcohols, whereas, the STY of total alcohols increased to a
certain value and then remained constant with increasing GHSV. Figure 25c
CA 02739142 2011-05-05
shows that GHSV had a small effect on total alcohols STY, compared to that of
T
and P.
[00178] Figures 26a, 26b, and 26c exhibit the dependency of operating
conditions (T, P, and GHSV) on hydrocarbons STY at H2 to CO molar ratio of 1.
As observed, the formation of hydrocarbons exponentially increases at high
reaction temperatures. These results combined with total alcohols STY suggest
that the produced alcohols are consumed to form hydrocarbons with synthesis
gas at higher temperatures. Hydrocarbon STY increased slightly with increasing
pressure, whereas, the hydrocarbon formation decreased with GHSV. Table 10
shows that the model fits well with the experimental results. The CO2
formation
model follows a similar trend as that of the hydrocarbon formation. Compared
to
that of hydrocarbons, higher STY of CO2 were observed at all experimental
conditions. Table 10 shows that the CO2 model fits with R2 value of 0.954.
(c) Effects of the temperature, pressure, and gas hourly space velocity on
selectivity of alcohols
[00179] The influence of the operating conditions T (275 to 350 C), P (800
to 1400 psig), and GHSV (2.4 to 4.2 m3 (STP)/(kg of cat.)/h) on selectivities
of
methanol, ethanol, higher alcohols, and total alcohols using H2 to CO molar
ratio
of 1 were investigated. There was good agreement between the simulated
results and the experimental observations (Table 12). The methanol selectivity
decreased monotonically with increasing temperature, but increased with
increasing pressure and GHSV. The ethanol (Figure 27), higher alcohols, and
total alcohols selectivities displayed a pronounced increase with increasing
temperature and reached a maximum value, suggesting that the significant
activity for the dehydration of alcohols takes place at higher temperatures.
With
increasing pressure, ethanol selectivity increased to a certain value and
remained constant, whereas, a maximum was obtained with increased GHSV
(Figure 27). The higher alcohols and total alcohols selectivity monotonically
CA 02739142 2011-05-05
56
increased with increasing pressure and GHSV. This discrepency between the
ethanol and higher alcohols selectivities at higher pressures and GHSVs is due
to the increasing ability of chain growth from ethanol to higer alcohols.
(d) Optimization of operating conditions
[00180] The optimum operating conditions using H2 to CO molar ratio of 1
were defined according to the following constraints: (1) Ethanol STY to be
maximum; and (2) ethanol selectivity to be maximum. The solution for the model
was obtained as follows: T = 330 C, P = 1320 psig (9.1 Mpa), GHSV = 3.8 m3
(STP)/(kg of cat.)/h. The experiments were performed at these operating
conditions, with both the ethanol STY and selectivity presented together with
the
model predictions. The difference of ethanol STY was around 3% and that of the
selectivity was less than 5%.
(e) Effects of H2 to CO molar ratio on higher alcohols synthesis from
synthesis gas
[00181] In this study, the H2 to CO molar ratio (0) was varied from 0.5 to
2.0 and the experiments were carried out using the optimum operating
conditions
of T, P, and GHSV reported in (d). Figure 28 depicts the influence of 0 on the
%
CO conversion, hydrocarbons STY, and CO2 STY. The results show that
increasing the 0 from 0.5 to 2.0 led to increased % CO conversion from 33.0 to
54.2%, suggesting that the catalyst activity is improved with O.
[00182] The hydrocarbons formation rate increased monotonically from
0.141 to 0.354 g/(g of cat.)/h, whereas the CO2 STY decreased monotonically
from 0.541 to 0.239 g/(g of cat.)/h with increasing 0 from 0.5 to 2Ø The
responses of methanol, ethanol, higher alcohols, and total alcohols formation
(Figure 29) show that the rate of methanol formation increased with increasing
0,
while the ethanol and higher alcohols STY revealed their maximum at O value
between 1 to 1.5. Figure 29 also shows that the total alcohols formation
increased to specific 0 and remained constant.
CA 02739142 2011-05-05
57
[00183] While not wishing to be limited by theory, these results can be
explained from the CO insertion mechanism of higher alcohols synthesis
reaction
55 The partial pressure of CO was high at low values of O, which resulted in
enhanced CO insertion and C-C chain growth favoring the formation of
compounds with a carbon number greater than 1. With increasing 0 value, the
partial pressure of H2 increased, resulting in the formation of C1 products,
such
as methanol and methane. Because of a decreased amount of higher alcohols
and hydrocarbons with a carbon number greater than 1, the water gas shift
reaction rate was low due to small water formation.
[00184] The selectivities of methanol, ethanol, and higher alcohols exhibit
similar trends as that of their STYs (Figure 30). Methanol selectivity
monotonically increased from 4.9 to 18.6 wt %, with increased 0 from 0.5 to
2Ø
A maxima was observed in the selectivity of ethanol and higher alcohols at
around O value of 1.25, whereas the total alcohols selectivity showed a
maximum at 0 value of approximately 1.5.
(fl Reproducibility study
[00185] Reproducibility of the experimental data was tested at optimum
operating T, P, and GHSV using O values of 1, 1.5, and 2, and the results
representing ethanol STY and selectivity are reported in Table 13. Some
experimental conditions were repeated to determine the t- and p- values. To
determine the effect of packing on the experimental results, the reactor was
reloaded with a fresh batch of catalyst and the experiments and repetitions
were
carried out. The unequal sample sizes equal variance Student's t test method
was used to determine reproducibility of the results. The results indicated
that the
calculated p-value associated with the t test was not small (> 0.05),
providing
evidence that the means are not different. This proves that the data are
reproducible with small (< 5)experimental errors.
CA 02739142 2011-05-05
58
Example 5: Intrinsic Reaction Kinetics of Higher Alcohols Synthesis from
Synthesis Gas over Sulfided Alkali-Promoted Co-Rh-Mo Trimetallic Catalyst
Supported on Multi-Walled Carbon Nanotubes
[00186] The heterogeneous catalytic reaction is associated with external
and internal diffusional resistances. The diffusion of the reactants or
products
between the bulk fluid and the external surface of the catalyst is known as
external resistance, and diffusion of the reactants from the external surface
(pore
mouth) to the interior of the particles and diffusion of the products from the
interior of the particles to the external surface is referred as internal
resistance.78
Reaction rates in the absence of these internal and external diffusion
resistances
are termed as intrinsic kinetics.79
Materials and Methods
(a) Catalyst preparation
[00187] The catalysts were prepared as described in Example 1. After
stabilization, the catalysts were palletized and then ground to different
particle sizes.
(b) Catalyst characterization
[00188] The contents of Mo, Co, and Rh of different particle size pellet
samples were determined using a Perkin-Elmer ELAN 5000 inductively coupled
plasma mass spectroscopy (ICP-MS) instrument as described in Example 1.
(c) Catalytic studies
[00189] The higher alcohols synthesis was tested in an experimental unit
(Figure 31), which had a single-pass tubular downflow fixed-bed reactor of 450-
mm length and 22-mm inside diameter, made of inconel tube. The reactor was
packed with 2 g of catalyst diluted with 12 ml of 90 mesh size silicon carbide
and
housed in an electric furnace controlled by a temperature controller. The
reactor
was pressurized with He to 500 psig (3.44 MPa) and the sulfidation, together
with
CA 02739142 2011-05-05
59
the reduction, was carried out for 6 h at 450 C at a heating rate of 2 C/min
using
a gas mixture containing 10 mole % H2S in H2 and a flow rate of 50 ml/min. The
temperature was then lowered to the reaction temperature, and the system
pressurized to the reaction conditions. The feed gas mixture (desired molar
ratio
of CO and H2 mixed with 10 mole % Ar) was passed through mass flow
controllers and the higher alcohols synthesis was carried out at steady-state
under the reaction conditions over a period of 24 h, after an initial
induction
period of 15 h. The product gas was cooled to 0 C and separated into gas and
liquid phases at the reaction pressure. The CO conversion and other gaseous
products were monitored with a time interval of 1 h. After an induction period
on
15 h, the liquids were removed from the condensers. The variation in gas
concentration is found to be little after an induction period, and hence,
constant
values of liquid concentrations are assumed during that reaction time. The
liquid
products were collected at the end of the reaction and analyzed with a Varian
3400 gas chromatograph equipped with a capillary column and a flame ionization
detector. The volume and weight of liquid products were measured to check the
mass balance. The gaseous products were analyzed online on a Shimadzu gas
chromatograph through a sampling valve. Using Ar as an internal standard, the
CO conversion was calculated and the overall mass balance of the reaction was
determined.
(d) Experimental design for intrinsic kinetics
[00190] Four parameters, such as reactor temperature (T), pressure (P),
gas hourly space velocity (GHSV), and H2 to CO molar ratio were varied using
four different levels in the ranges of 275-350 C, 800-1400 psig (5.52-9.65
MPa),
2.4-4.2 m3 standard temperature and pressure (STP)/(kg of cat.)/h, and 0.5-
2.0,
respectively. A Taguchi orthogonal array method was used to develop the
experimental plan to analyze the intrinsic kinetics for higher alcohols
synthesis
from synthesis gas, and the set of experiments are shown as set 1 in Table 14.
Design-Expert software, version 6Ø1 was used to design the set of
experiments
CA 02739142 2011-05-05
performed in this study. The experiments were performed randomly, and the
center-
point experiment was repeated after every four runs during the activity tests
to verify
the catalyst stability. Additional experiments were designed using a H2 to CO
molar
ratio of 1.25 and performed at the conditions as listed as set 2 in Table 14.
Each run
was performed over a period of 24 h using 2 g of catalyst. The catalytic
activity and
product selectivity data were calculated after an induction period of 15 h.
The catalyst
was kept under a constant inert gas (He) flow of 50 ml/min between the runs,
when it
was necessary to shut down the reactor.
Results and Discussion
(a) External mass-transfer diffusion
[00191] The external mass-transfer diffusion can be eliminated by
decreasing the mass-transfer boundary layer thickness, which is the distance
from a solid object to the region where the concentration of the diffusing
species
reaches 99% of the bulk concentration. This can be eliminated by increasing
the
velocity past the particle or using very small particles.78 To determine the
effect of
external mass transfer on the performance of the K-promoted Co-Rh-
Mo/MWCNTs catalyst for CO hydrogenation, sample pellets of different particle
size ranges of 707-841, 420-500, 210-297, and 147-210 pm with average particle
sizes of 0.774, 0.460, 0.254, and 0.179 mm, respectively, were prepared.
[00192] To confirm the homogeneous distribution of active sites through the
pellet and from pellet to pellet, the samples were collected from different
catalyst
pellets and the metal contents of these samples were analyzed using ICP-MS.
The results were given in Table 15 along with the targeted compositions. From
this table, it is clear that the measured contents of the prepared catalysts
are
slightly lower compared to targeted values, which may be due to the
hygroscopic
nature of precursors. The metal contents of different sample pellets are found
to
be comparable, confirming the uniform distribution of active sites through the
catalyst.
CA 02739142 2011-05-05
61
[00193] The effect of the particle size on external mass-transfer diffusion
was studied by performing the experiments at an inlet pressure of 1320 psig
(9.1
MPa), flow rate of 120 ml/min, and reaction temperatures in the range of 275-
350 C. For each experiment, 2 g of catalyst was used and the reaction was
carried out using a feed gas mixture of CO (40 mole %), H2 (50 mole %), and Ar
(10 mole %). Figures 32 and 33 show the % CO conversions and total alcohols
space time yield (STY) of the catalysts with different particle sizes at
different
temperatures, respectively. The %CO conversion and total alcohol STY
increased linearly at all reaction temperatures with decreasing catalyst
average
particle size from 0.774 to 0.254 mm, but no significant change was observed
in
the reaction with further decreasing particle size to 0.179 mm. These results
suggested that the catalyst particle size has a great influence on the higher
alcohols synthesis from synthesis gas and that the mass transfer across the
boundary layer limited the rate of reaction, using the catalyst with a
particle size
greater than 0.254 mm. Use of the catalyst with an average particle size less
than 0.254 mm ensured that the film resistance to external mass transfer was
negligible for the kinetic parameter estimation experiments, and hence, the
catalyst with a particle size in the range of 147-210 pm was selected.
[00194] The Frossling correlation80 is used in flow around spherical particles
to obtain the relation between the particle size (dp) of the catalyst, mass-
transfer
coefficient (kc), and boundary layer thickness (b). The required parameters
and
constants for the estimation of Frossling correlation are calculated. The mass-
transfer correlation is given as follows:
A = 2 + 0.6(Re)'~'2 (Sc) ~~3 (1)
Sh = k~ P (2)
De
Re = pudn (3)
P
CA 02739142 2011-05-05
62
Sc (4)
pD,
where kc is the average mass transfer coefficient of a reactant from the bulk
flow
to catalyst surface (m/s), dp is the average diameter of the catalyst particle
(m),
De is the effective diffusivity for a binary gas mixture (m2/s), u is the free
stream
velocity of fluid (m/s), p is the gas density (kg/m3), and p is the gas
dynamic
viscosity (kg/(m-s)).
[00195] Table 16 shows results of the mass-transfer coefficient of carbon
monoxide from the bulk flow to the surface of the catalyst particle (k ) and
the
boundary layer thickness (5) calculated using the Frossling correlation. From
these results, it is observed that decreasing dp of catalyst particles from
0.774 to
0.179 mm, increased kc value about 3 times more and decreased 5 about 3 times
less than that of the initial value. It is also noted that the temperature has
a
negligible effect on the external mass-transfer diffusion.
[00196] The effect of the feed gas flow rate on external mass-transfer
diffusion was studied by performing the experiments at an inlet temperature of
325 C, pressure of 1320 psig (9.1 MPa), and H2 to CO molar ratio of 1.25 using
2
g of catalyst with average particle size of 0.179 mm. The variation in % CO
conversion with flow rate is given in Figure 34. It is expected that, in the
case of
existing external mass-transfer resistance, the boundary layer thickness
becomes reduced with an increased flow rate and results in the enhanced CO
conversion at higher flow rates. From Figure 34, it is observed that the % CO
conversion decreased monotonically from 52 to 42% with an increased flow rate
from 80 to 120 ml/min, which resulted because of the short contact time
between
the reactants at high flow rates. k, and 5 values were calculated for
different flow
rates, and the results are given in Table 17. It is clear from this table that
the flow
rate has a negligible effect on external mass-transfer diffusion under the
investigated operating conditions using the sample pellets of average particle
diameter of 0.179 mm.
CA 02739142 2011-05-05
63
(b) Internal mass-transfer diffusion
[00197] The Weisz-Prater criterion (Cwp) is used to estimate the internal mass-
transfer resistance in heterogeneous catalytic reactions.18 If CWP 1, there
is no
internal diffusion limitation, and if Cwp 1, internal diffusion limits the
reaction
severely.78 This criterion is given as follows:
- (r,4 * *R 2
CWP ),,ns Pc (5)
De CA,
where (rA)Obs is the reaction rate per unit mass of catalyst, p,, is the
catalyst
density, R is the particle radius, CA, is the surface concentration of
reactant A,
and De is the effective diffusivity.
[00198] The value of Cwp was calculated for the catalysts with average
particle diameter of 0.179 mm at 300 C. The Cwp value of this parameter was
obtained as 0.007, which is far less than 1. This confirms that internal
diffusion
limitation is negligible on the catalyst with the average particle diameter of
0.179
mm.
(c) Intrinsic kinetics
[00199] The analysis of liquid products indicates that the alcohols likely
followed the CO insertion mechanism, forming linear alcohols. Methanol,
ethanol,
n-propanol, and n-butanol are the major products together with other higher
alcohols. Very little water (<l% by weight) was found in the liquid product,
and
hence, the concentration of water was neglected. The analysis of exit gas
indicates that methane is the major hydrocarbon component apart from CO2 as
well as unconverted CO and H2.
[00200] The reaction scheme suggested by Santiesteban et al.9 for the
production of alcohols from synthesis gas over MoS2 catalysts was used to
determine the intrinsic reaction kinetics. It is difficult to obtain a
statistically valid
model for such an extremely complex reaction scheme; hence, the simplified
reaction
CA 02739142 2011-05-05
64
scheme was assumed. The liquid and gas streams were simplified into a selected
number of components, namely, CO, H2, CO2, methanol, and ethanol, as well as
pseudo-components, Hyd that represents methane and higher hydrocarbons, and
HAC3+ that represents higher alcohols (alcohols with carbon number greater
than 2).
All the reactions were assumed to be stoichiometric, and the simplified
reaction
scheme is as shown below81:
CO + 2H2 H CH3OH (6)
2CH3OH -~ C2H5OH + H2O (7)
(NHA -2)CH3OH + C2H5OH --~ HAC3+ + (NHA - 2)H20 (8)
NHCCO + (2NHC + 1)H2 -4 Hyd + NHCH2O (9)
CO+H2O,)CO2+H2 (10)
where NHA and NHC stand for the average carbon atom number of the pseudo-
components HAC3+ and Hyd, respectively.
[00201] In the above reaction scheme, the formation of methanol and
hydrocarbons are obtained directly from CO and H2. It is assumed that
hydrocarbon
products are composed exclusively of methane. Methanol formation and the water-
gas shift (WGS) reaction are assumed to be in thermodynamic equilibrium, and
other
reactions are assumed to be irreversible. 82 The formation of ethanol and
higher
alcohols were assumed to follow stepwise chain growth alcohols by taking
methanol
as the recurrent C, reactant; that is, one mole of ethanol is produced from
two moles
of methanol and one mole of propanol is obtained from one mole of methanol and
one mole of ethanol, etc. The present reaction scheme is similar to the lumped
kinetic model, which accounts for the global formation of higher oxygenates
suggested by Tronconi et al.83
[00202] The power law model was used for the reaction between CO and H2
on the catalyst surface, because this model is simple and widely used to
predict the
reaction rate for the higher alcohols synthesis reaction. 84,85 A reversible
kinetic
CA 02739142 2011-05-05
expression was used for the methanol synthesis and the WGS reaction. Ideal gas
behaviour was assumed with WGS reaction, whereas the non-ideal behavior of
methanol was considered.89 Ethanol, higher alcohols, and hydrocarbon
formations
were represented using irreversible kinetic expressions.
[00203] The plug-flow reactor was used in the kinetic study of the higher
alcohols synthesis reaction over the alkali-promoted trimetallic Co-Rh-Mo
catalyst supported on MWCNTs. As discussed in the previous section, the
catalyst particle size in the range of 147-210 pm was selected to eliminate
the
external and internal mass-transfer resistances and the reactor was regarded
as
isothermal. Differential mole balance equations were used and were solved by
using ode45 routines in MATLAB, and, simultaneously, the sum of the squares
function was minimized by using fminsearch. The kinetic parameters were
estimated by fitting the experimental data in the sum of the squares function
and
minimizing the errors. The residual error values obtained at 275, 300, 325,
and
350 C are 0.0954, 0.0335, 0.0874, and 0.0395, respectively. Arrhenius plots
are
drawn for obtaining activation energies and frequency factors from the kinetic
parameters, and the values shown in Table 18. Figures 35 to 39 show the fit
between observed values and the predicted model values of methanol, ethanol,
higher alcohols, hydrocarbons, and carbon dioxide, respectively. The R2 values
by the models show a good fit with the experimental results.
[00204] It was observed that the CO conversion, hydrocarbon formation
rate, and the WGS reaction rate increased monotonically with an increased
temperature, whereas, methanol formation decreased monotonically with an
increased temperature from 275 to 350 C. A maxima is observed in ethanol and
higher alcohols formation at 330 C. As shown in Table 16, the activation
energy
of hydrocarbons and carbon dioxide were higher than that of the alcohols. This
is
because the hydrocarbon formation rate and the water gas shift reaction rate
both increased at higher temperatures. The activation energy of alcohols is
observed in the following order: methanol < ethanol < higher alcohols. This
CA 02739142 2011-05-05
66
explains that an increasing temperature favors the conversion of lower
molecular-weight alcohols to higher alcohols. Christensen et al.85 explained
that
an increased temperature favors the high CO surface coverage on the catalyst
which favors the improved rate of the CO insertion step and yields chain
growth.
This is an uncommon behavior for such chain growth reactions.
[00205] Table 19 compares the activation energies for methanol, ethanol,
higher alcohols, and hydrocarbons obtained over the alkali-promoted
trimetallic Co-
Rh-Mo catalyst supported on MWCNTs to those of values from available
literature.
The increase in activation energy with the alcohol carbon number was in
agreement
with the literature.85 The activation energies of ethanol and higher alcohols
obtained
over the Co-Rh-Mo-K/MWCNT catalyst were low compared to those values reported
in the literature. Low activation energies of alcohols might be possible
because of the
structural modification of Mo species with the promotion of K, Co, and Rh,
which
favor the formation of small particles uniformly dispersed inside and outside
the
straight pores of the MWCNTs support. This explains that the Co-Rh-Mo-K/MWCNT
catalyst performance is better compared to that of the catalysts that have
been
studies so far and are available in the open literature.
Example 6: Deactivation Studies of Alkali-Modified Trimetallic Co-Rh-Mo
Sulfided Catalysts for Higher Alcohols Synthesis from Synthesis Gas
Materials and Methods
(a) Preparation of catalysts
[00206] Both commercial catalyst supports, MWCNTs (M.K. Nano, surface
area-178 m2/g and pore volume-0.54 cc/g) and activated carbon (Aldrich,
surface
area-655 m2/g and pore volume-0.93 cc/g), were treated with 30% HNO3 reflux at
100 C overnight and washed with distilled water several times, followed by
drying
at 120 C for 6 h. The support, MWCNTs has a surface area of 220 m2/g and pore
volume of 0.66 cc/g, whereas, the activated carbon support exhibits a surface
area of 676 m2/g and pore volume of 0.97 cc/g. Ammonium heptamolybdate
CA 02739142 2011-05-05
67
tetrahydrate (AHM), potassium carbonate, cobalt acetate tetrahydrate, and
rhodium chloride hydrate were used as precursors for Mo, K, Co, and Rh,
respectively. The catalysts were prepared by conventional incipient wetness
method, as described in the previous Examples.
(b) Characterization of fresh and spent catalysts
[00207] The morphology of both the fresh and spent catalysts was
characterized by transmission electron microscopy (TEM) investigations, using
a
Philips CM20 (100 kV) transmission electron microscope equipped with a
NARON energy-dispersive spectrometer with a germanium detector.
[00208] The content of Mo, Co, and Rh of the oxide catalysts were
determined using a Perkin-Elmer ELAN 5000 inductively coupled plasma mass
spectroscopy (ICP-MS) instrument.
[00209] The surface area, pore volume, and average pore diameter of fresh
catalysts in oxide and sulfide forms, as well as the spent catalysts were
measured by N2-physisorption at 77 K using a Micromeritics ASAP 2000.
Approximately 0.2 g of sample was used for each analysis. The moisture and
other adsorbed gases present in the sample were removed before analysis by
degassing the sample at 200 C for 2 h under 66.7 Pa (500 mm Hg). The sample
was then evacuated at 2.67 Pa (20 dam Hg) before N2 adsorption.
[00210] The carbon monoxide uptake on the fresh and used catalysts was
measured using the Micromeritics ASAP 2000 instrument. Prior to the CO
chemisorption measurement 0.2 g of sample was sulfided in situ, using 10
mole % H2S in H2 at 400 C for 4 h. The sample was then evacuated at 120 C
until the static pressure remained less than 6.6 x 10"4 Pa. Chemisorption was
performed by passing pulses of CO over the sample to measure the total gas
uptake at 35 C. The CO uptake (pmole/g of cat.) measured from CO chemisorption
is equivalent to the number of active metal atoms that are accessible to the
reactant
CA 02739142 2011-05-05
68
molecules. The stoichiometric coefficient (CO to metal ratio) of 1 was used,
and the
extent of reduction was assumed to be 100% in metal dispersion calculations.
[00211] Powder X-ray diffraction (XRD) analysis patterns of oxide and
sulfide forms of both the fresh and spent catalysts were recorded on a Rigaku
X-
ray diffraction instrument with nickel filtered Cu Ka radiation (A = 0.1541
nm).
Each sample was scanned at a rate of 0.05 /s, with 20 varying from 10 to 80 .
To obtain the XRD patterns in sulfided form, the catalysts were first sulfided
for 6 h
at 450 C, at a heating rate of 2 C/min using a gaseous mixture containing 10
mole % H2S in H2 at a flow rate of 50 ml/min. After sulfidation, the catalysts
were
cooled to room temperature in a flow of He and the sample was transferred to
sample holders under protection of He.
[00212] To study the reducibility of the fresh and spent catalysts,
temperature programmed reduction (TPR) profiles of the catalysts were
performed. For each analysis, approximately 0.2 g of sample was used, which
was first purged in 50 cm3 (STP)/min flow of He at 170 C to remove traces of
water, and then cooled to 40 C. The TPR of each sample was performed using a
mole % H2 in Ar stream at a flow rate of 50 cm3 (STP)/min and a heating ramp
rate of 10 C/min from 40 C to 650 C. Hydrogen consumption was monitored by a
thermal conductivity detector (TCD) attached to a Micromeritics AutoChem II
chemisorption analyzer. During the analysis the effluent gas was passed
through
a cold trap placed before the TCD in order to remove water from the exit
stream
of the reactor.
[00213] The amount of carbon deposition after 720 h of continuous higher
alcohols synthesis was analyzed by performing thermogravimetric analysis (TGA)
of fresh and spent catalyst using a Perkin-Elmer thermogravimetric (TG)
differential thermal analyzer (DTA) under air flow of 40 ml/min. The samples
were
heated in a platinum sample holder from room temperature to 600 C with a
heating rate of 5 C/min.
CA 02739142 2011-05-05
69
(c) Catalytic durability studies
[00214] The catalytic durability studies for conversion of synthesis gas to
higher alcohols were performed using the feed gas mixture CO (40 mole %), H2
(50 mole %), and Ar (10 mole %) in a single-pass tubular downflow fixed-bed
reactor under the reaction conditions of 330 C, 9.1 MPa (1320 psig), and 3.8
m3
(STP) /(kg of cat.)/h over a period of 720 h. The detailed description about
the
high pressure reaction set up used in this study is as discussed in the
previous
examples. Prior to the reaction, the catalyst was reduced and sulfided, for 6
h
at 450 C at a heating rate of 2 C/min using a gas mixture containing 10 mole %
H2S in H2 at a flow rate of 50 ml/min. The product gas was separated into gas
and liquid phases inside the condensers at 0 C and reaction pressure. The
liquid
products were collected from the cold traps every 12 h during the first 2 days
and
then obtained after every 24 h. The sulfur content of the liquid product
obtained
at different time intervals was measured using the combustion-fluorescence
technique of the ASTM 5463 method. The instrumental error for S analysis was
approximately 3%, based on analyzing standard solutions of known composition.
The liquid products were analyzed with a Varian 3400 gas chromatograph
equipped with a capillary column and a flame ionization detector (FID). The
gaseous products were analyzed online on a Shimadzu gas chromatograph
through a sampling valve for every 1 h. The results obtained were within the
experimental error of 2.5%.
[00215] After 720 h of the higher alcohols synthesis, the flow of synthesis
gas was switched off, and the catalyst was re-sulfided and reduced in a flow
rate
of 50 ml/min of 10 mole % H2S in H2 at 450 C for 6 h. The higher alcohols
synthesis was again carried out under the same conditions, as discussed above
for 24 h. The temperature of the reactor was lowered to room temperature and
the catalytic bed was treated by helium flow for 3 h at room temperature to
washout the H2S and synthesis gas present inside the reactor. The catalyst was
CA 02739142 2011-05-05
then passivated with pulses of dry air to stop further oxidation. The spent
catalyst
was removed from the reactor and characterized extensively.
Results and Discussion
(a) Characterization of fresh and spent catalysts
[00216] TEM images of the fresh and spent alkali-modified trimetallic Co-Rh-
Mo catalysts supported on MWCNTs were recorded and shown as Figures 40a and
40b, respectively. The tubular morphology of the grapheme layers make MWCNTs a
different support compared to activated carbon. The TEM image of the fresh
MWCNT-supported catalyst (Figure 40a) revealed that the metal species are well
dispersed both inside the carbon nanotubes and on the outside of the tube
walls in
the particle size range of 1 to 5 nm. Figure 40b shows that sintering occurs
on the
particles located on the outer surface of the MWCNTs, whereas the size of the
particles inside the tubes is almost similar to that of the fresh catalyst.
The rr-electron
density creates a deviation in the concave inner and convex outer surface of
the
graphite layers, leading to an electron-deficient interior and an electron-
enriched
exterior surface.86 This results in a strong interaction of metal species with
the
support on the particles located on the inner surface of the MWCNTs, compared
to
their outer layers. The little or no mobility of the particles inside the
tubes prevents the
occurrence of sintering.87
[00217] Figures 41 a and 41b show the TEM images of fresh and spent Co-
Rh-Mo-K catalysts supported on activated carbon. Some of the metal species are
inside the pores and a considerable amount of agglomerates are formed on the
surface of the microporous activated carbon support (Figure 41 a). The TEM
image of
the spent catalyst (Figure 41 b) shows the formation of large agglomerates,
resulting
from the large sintering rate of metal species on the catalyst. Iranmahboob et
a!.36
explained that agglomeration of cobalt and sulfur takes place after exposure
to
synthesis gas on the catalyst surface, leading to the formation of square-like
planes
CA 02739142 2011-05-05
71
of cubic crystallites (Co9S8). These results confirm that the agglomeration of
catalytic
species is high on the activated carbon support compared to that of MWCNTs.
[00218] Table 20 presents the Co, Rh, and Mo contents of the fresh and spent
catalysts measured by ICP-MS, along with the targeted compositions. Due to the
hygroscopic nature of precursors, the measured contents of the catalysts are
slightly low compared to targeted values. Deviation in the targeted and
measured
metal contents is high over the activated carbon-based catalysts compared to
the
MWCNT-supported catalysts, indicating that the concentration of metal
particles is
not uniform on this support. ICP analyses revealed that the metal content of
the
spent catalysts was close to that of the fresh catalysts.
[00219] Results of the textural characteristics such as surface area, total
pore volume, and average pore diameter obtained over the fresh, sulfided, and
spent catalysts are given in Table 20. The MWCNT-supported alkali-promoted
trimetallic Co-Rh-Mo catalyst showed a BET surface area of 68 m2/g and a total
pore volume of 0.24 cm3/g. Upon sulfidation of this catalyst, the BET surface
area
and pore volume increased to 79 m2/g and 0.29 cm3/g, respectively. After 720 h
of
higher alcohols synthesis, both the catalyst BET surface area and pore volume
decreased to 71 m2/g and 0.26 cm3/g, respectively. After impregnating the
metal
species, a drastic fall in surface area was observed over the activated carbon-
supported catalyst. The activated carbon-supported alkali-promoted trimetallic
catalyst showed a BET surface area and pore volume of 97 m2/g and 0.16 cm3/g,
respectively. These results suggest that pore blocking of the activated carbon
by
the metal species is high compared to that of MWCNTs, due to the microporous
nature of the activated carbon support.
[00220] Similar to the MWCNT-supported catalyst, sulfidation of the
activated carbon-supported Co-Rh-Mo-K catalyst improved both the BET surface
area and pore volume. Sulfidation causes reduction in particle size of the
metal
species that decreases the blocking extent of the support, resulting in
improved BET
surface area and pore volume. After 720 h over the spent activated carbon-
CA 02739142 2011-05-05
72
supported catalyst, a BET surface area of 85 m2/g and pore volume of 0.10
cm3/g
were observed. From these results, it is clear that sintering of the metal
species
and pore blockage due to coke deposition during higher alcohols synthesis is
high on the activated carbon-supported catalyst, causing a large decrease in
both BET surface area and pore volume, compared to that of the MWCNT-
supported catalyst.
[00221] Table 20 also gives the results of the CO chemisorption
measurements. The CO uptake on the fresh alkali-modified Co-Rh-Mo trimetallic
catalysts supported on MWCNTs and activated carbon was 237 and 137 pmole/(g
of cat.), respectively. The MWCNT-supported catalyst outperformed the
activated
carbon-supported catalyst, confirming that the support plays an important role
on CO
hydrogenation capability. Metal dispersions observed on the alkali-modified
trimetallic
catalysts supported on MWCNTs and activated carbon were 48% and 28%,
respectively. MWCNTs have the advantage of well-defined hollow interiors and
uniform straight pores with a large pore size, providing uniform distribution
of metal
species to obtain high dispersion on the support. The CO uptake value and
metal
dispersion for the spent catalyst supported on MWCNTs are slightly lower (7%
and 6%, respectively) than that of the fresh catalyst. The spent catalyst
supported on activated carbon was found to be 43% less in both CO uptake
value and dispersion of metal species compared to that of the fresh catalyst.
As
mentioned earlier, sintering of metal species and pore blockage due to coke
deposition might be responsible for low metal dispersions of the spent
catalyst
supported on activated carbon.
[00222] Figures 42 and 43 show the XRD patterns of the MWCNTs and
activated carbon-supported alkali-modified trimetallic Co-Rh-Mo catalysts
measured in oxidized and sulfided form, together with the spent catalysts
after 720
h of higher alcohols synthesis. The JCPDS chemical spectra data bank was used
to detect the most probable phases present in the samples, and the results of
the
possible crystal phases with their corresponding reflection planes are given
in
CA 02739142 2011-05-05
73
Table 19. The reflections of the graphite phase are observed at d spacing of
3.347
in both the MWCNTs and activated carbon supports.88 The characteristic
reflections
corresponding to the crystalline structure of MoO3 are observed at 20 value of
40.2
in the XRD patterns of the oxidized form of catalysts supported on MWCNTs and
activated carbon.89 Peaks corresponding to the characteristic reflections of
different
K-Mo-O phases, such as KM04O6 (d-spacing of 5.366 and 2.403), K2M07O20 (d-
spacing of 3.770), and K2Mo2O7 (d-spacing of 3.222) are also observed.90,91,92
[00223] The formation of MoS2 crystallites are observed at d-spacing of 6.110,
2.707, 2.199, and 1.570 in the XRD pattern of the sulfided catalysts (Figures
42b
and 43b). The characteristic reflections of the K-Mo-S species are observed at
d-
spacing of 3.100, 3.020, and 2.780. The peak corresponding to the
characteristic of
bulk Co9S8 particles is observed at d-spacing of 1.751. XRD patterns of the
spent
catalysts supported on MWCNTs and activated carbon are shown in Figures 42c
and
43c, respectively. There is no significant change in the intensity of the
peaks
corresponding to the K-Mo-S mixed phases, but increased peak intensities of
the
MoS2 and Co9S8 phases were observed. These results confirm that sintering of
metal
sulfide crystallites such as M0S2 and Co9S8 takes place upon exposure to the
synthesis gas, leading to the agglomeration of these species on the support.
Compared to the MWCNT-supported spent catalyst (Figure 42c), a significant
increase in peak intensity for the MoS2 and Co9S8 species is noted in the
spent
catalyst supported on activated carbon (Figure 43c), indicating that particle
size
increased with time on stream for 720 h. This may be due to the sintering of
metallic
particles during the reaction, as a result of the poor interaction between
metal
particles and the support.
[00224] The activation of the fresh and spent alkali-modified trimetallic Co-
Rh-
Mo catalysts supported on MWCNTs and activated carbon in a hydrogen
atmosphere was proven by TPR experiments and shown in Figures 44 and 45,
respectively. The H2-TPR studies of the fresh catalyst supported on MWCNTs
(Figure 44a) reveal the main reduction peak at 328 C, due to the complete
reduction
CA 02739142 2011-05-05
74
of bulk MoO3 species to lower oxidation state. A shoulder peak in the
temperature
range 250-300 C is due to the reduction of bulk C003-related species. A small
peak
attributed to the reduction of Rh species is noted in the temperature range 97
C.
Over the spent catalyst supported on MWCNTs (Figure 44b), the reduction of Mo
species took place in two different steps; first the reduction of octahedral
coordinated
Mo (Mo+6) species to tetrahedral coordinated Mo (Mo+4) species occurs at 326
C,
followed by the reduction of Mo+4 species to a lower oxidation state at 601'C.
The
peak corresponding to the reduction of Co species shifted to a lower
temperature of
197 C, indicating that the easier reduction of the cobalt occurred in the
spent catalyst
compared to the fresh. The easier reduction of Co species can be explained by
the
formation larger particles on the outer surface of the nanotubes, which is
evident from
TEM image of the spent catalyst supported on MWCNTs (Figure 40b). No peaks
corresponding to the reduction of Rh species were present, indicating that Rh
exists
in completely reduced form over the spent catalyst. These results coupled with
the
XRD pattern (Figure 42c) confirm that the sintering of Co species is high
after
exposure of synthesis gas on the catalyst surface, whereas the Mo and Rh
species
are quite stable with little or no sintering over the alkali-promoted
trimetallic Co-Rh-
Mo catalyst supported on MWCNTs.
[00225] Two main reduction peaks are observed in the TPR studies of the
fresh activated carbon-supported alkali-modified trimetallic Co-Rh-Mo catalyst
(Figure
45a), with the low temperature reduction peak appearing around 321 C and the
high
temperature peak around 640 C. No peak is observed representing the reduction
of
Co species, but the small peak at 94 C represents the reduction of Rh species.
The
peak representing the reduction of Mo+6 to Mo+4 oxidation state shifted to
higher
temperatures over the spent catalyst supported on activated carbon (Figure
45b).
These results indicate that the interaction of Mo species occurred with the
activated
carbon support after the catalyst was exposed to synthesis gas. Compared to
the
fresh catalyst, an extra peak was observed at 216 C representing the presence
of Co
species over the spent catalyst supported on activated carbon. As seen from
the
CA 02739142 2011-05-05
TEM image (Figure 41b) and XRD patterns (Figure 43c) of the spent catalyst,
agglomeration of metal species were found to be high on the surface of
activated
carbon, due to the sintering of active phases.
[00226] The thermo-gravimetric (TG) profiles of the temperature-
programmed oxidation (TPO) in air of the fresh and spent catalysts supported
on
MWCNTs are shown in Figure 46. The slight weight loss over the catalysts
occurring at around 100 C was probably resulted from the evaporation of
moisture. The weight loss over the MWCNT-supported spent catalyst (Figure
46b) in the range of 100 to 400 C might be due to the oxidization of S
species.
However, the carbon deposits were oxidized at around 450-600 C (Figures 46a
and 46b). The TG profiles of the fresh and spent catalysts supported on
activated
carbon revealed that activated carbon support is more susceptible to coke
formation and deactivation (Figures 47a and 47b). These result confirmed that
coke deposition is high on the activated carbon-supported catalyst compared to
that of the catalyst supported on MWCNTs.
[00227] Catalytic durability studies
[00228] The sulfided alkali-promoted trimetallic Co-Rh-Mo catalysts supported
on MWCNTs and activated carbon were tested for the synthesis of higher
alcohols
from synthesis gas under similar conditions of 330 C, 9.1 MPa (1320 psig), and
3.8
m3 (STP)/(kg of cat.)/h. The profiles of % CO conversion as functions of time
on
stream for 720 h, with a synthesis gas feed containing 40 mole % CO, 50 mole %
H2,
and 10 mole% Ar obtained over alkali-modified trimetallic Co-Rh-Mo catalysts
supported on MWCNTs and activated carbon are shown in Figures 48a and 48b,
respectively. Over the MWCNT-supported catalyst, two different deactivation
steps
are observed; the % CO conversion dropped by 10% (from 58% to 52%) during the
first 12 h and remained almost constant with % CO conversion dropping by only
1.9% for the remaining time-on-stream of higher alcohols synthesis. Three
different
deactivation steps are distinguishable over the activated carbon-supported
catalyst (1)
during the first 36 h, the % CO conversion dropped by 21% (from 43% to 34%);
(2)
CA 02739142 2011-05-05
76
during 36 to 350 h, the % CO conversion dropped by 9% (from 34% to 31 %); and
(3)
during 350 to 720, the % CO conversion dropped by 3% and almost reached a
plateau region.
[00229] Figures 49a and 49b present the total alcohols STY changes with time
on stream of continuous higher alcohols synthesis for a period of 720 h
obtained over
alkali-modified trimetallic Co-Rh-Mo catalysts supported on MWCNTs and
activated
carbon, respectively. In Table 20, the alcohols formation rate values
evaluated after
reaction periods of 12, 24 and 720 h, which refer to the catalyst weights,
surface area
and active sites under the hypothesis of differential reactor are reported.
The total
alcohols STY increased from 0.256 g/(g of cat.)/h after a 12 h reaction period
to
0.281 g/(g of cat.)/h after 24 h over the MWCNT-supported catalyst and
remained
almost constant over the remaining reaction time (Figure 49a). The STY of
total
alcohols over the activated carbon-supported catalyst, increased from 0.194 to
0.209
g/(g of cat.)/h for samples collected from 12 to 36 h of time-on-stream, and
decreased slowly to 0.193 g/(g of cat.)/h before it leveled off (Figure 49b).
[00230] The change in total hydrocarbon STY with time-on-stream for a
continuous reaction time of 720 h over the alkali-modified trimetallic
catalysts
supported on MWCNTs and activated carbon are given in Figures 50a and 50b,
respectively. Figure 50a shows that during the first 12 h reaction time, the
total
hydrocarbon STY decreased from 0.276 to 0.249 g/(g of cat.)/h and remained
almost
steady state in the next 710 h over the catalyst supported on MWCNTs. A rapid
decrease in the STY of total hydrocarbons from 0.239 to 0.206 g/(g of cat.)/h
occurred during the first 30 h of time-on-stream and then slowly leveled off
to a
constant value of 0.191 g/(g of cat.)/h (Figure 50b).
[00231] The CO2 produced in the reactor during 720 h of continuous operation
over the MWCNTs and activated carbon-supported catalysts are reported in
Figures
51a and 51b, respectively. The water-gas-shift (WGS) reaction rate was almost
constant during the entire reaction period over the MWCNT-supported catalyst,
whereas over the catalyst supported on activated carbon a drastic fall was
noticed in
CA 02739142 2011-05-05
77
the WGS reaction for first 30 h and then slowly leveled off to a constant
value due to
pore blockage of the support due to the sintering of catalyst species.
[00232] Regeneration of the spent catalyst at 4500C increased the % CO
conversion from 51 to 56% and over the catalysts supported on MWCNTs and
activated carbon it increased from 29 to 36%, respectively. The total activity
recovery
over the MWCNTs and activated carbon-supported catalysts after regeneration is
close to the total activity loss during the first deactivation step (about 10%
and 19%,
respectively). The addition of Co (Rh) to MoS2 catalysts leads to the
formation of
active phase Co (Rh)-Mo-S that has a dual promotion effect of enhancing the
activity
by increasing S-vacancies and reducing the deposition of coke due to the
improved
hydrogenation rate of the coke ingredients.93 The catalyst deactivation that
occurred
after the first step is due to the sintering of metal sulfide species on the
support,
which is an irreversible process.94 Baghalha et al.95 observed the loss of the
Co-Mo-
S active phase during hydrodesulfurization of a naphtha stream that caused
about
19% of permanent catalyst activity deactivation during the first deactivation
step. The
present results demonstrate that the permanent loss of the active phase was
negligible over the alkali-promoted trimetallic catalyst for higher alcohols
synthesis
and the recoverable activity loss can be assigned to the loss of unstable
sulfur ions
from the edges of metal sulfide crystallites. This study revealed that MWCNT
is a
novel catalyst support to decrease sintering, metal support interaction and
coke
formation during catalytic process.
[00233] Table 21 compares the activities of sulfided 4.5 wt% Co, 1.5 wt% Rh,
15 wt% Mo and 9 wt% K supported on MWCNTs and activated carbon with those of
other catalysts discussed in the literature. The catalyst with the highest
activity from
each work was selected for comparison purposes. This table indicates that the
sulfides alkali-modified Co-Rh-Mo catalysts in the present work perform better
than
those reported in the literature.
[00234] While the present application has been described with reference to
what are presently considered to be the preferred examples, it is to be
CA 02739142 2011-05-05
78
understood that the application is not limited to the disclosed examples. To
the
contrary, the application is intended to cover various modifications and
equivalent
arrangements included within the spirit and scope of the appended claims.
[00235] All publications, patents and patent applications are herein
incorporated by reference in their entirety to the same extent as if each
individual
publication, patent or patent application was specifically and individually
indicated
to be incorporated by reference in its entirety. Where a term in the present
application is found to be defined differently in a document incorporated
herein
by reference, the definition provided herein is to serve as the definition for
the
term.
FULL CITATIONS FOR DOCUMENTS REFERRED TO IN THE APPLICATION
1 Anderson, R. B. The Fischer-Tropsch Synthesis, Academic Press Inc., Orlando,
1984.
2 Mahdavi, V.; Peyrovi, M. H.; Synthesis of C1-C6 alcohols over copper/cobalt
catalysts: Investigation of the influence of preparative procedures on the
activity
and selectivity of Cu-Co2O3/ZnO-AI203 catalyst. Catal. Commun. 2006, 7, 542-
549.
3 McCutchen, M. S. Synthesis of higher alcohols from carbon monoxide and
hydrogen in a slurry reaction, Ph.D. Dissertation, North Carolina State
University,
Raleigh, NC, 1992.
4 Doan, P. T. Characterization of Cu-Co-Cr-K catalysts, M.Sc. Dissertation,
Mississippi State University, Starkville, MI, 2001.
Iranmahboob, J. Formation of ethanol and higher alcohols from syngas, Ph.D.
Dissertation, Mississippi State University, Starkville, MI, 1999.
6 Smith, K. J.; Anderson, R. B. The higher alcohol synthesis over promoted
copper/zinc oxide catalysts. Can. J. Chem. Eng. 1983, 61, 40-45.
Sugier, A.; Freund, E. Process of manufacturing alcohols and more particularly
CA 02739142 2011-05-05
79
saturated linear primary alcohols from synthesis gas. U.S. Patent 4,291,126,
Sep
22, 1981.
8 Murchison, C. B.; Murdick, D. A. Process for producing C2-C4hydrocarbons
from carbon monoxide and hydrogen. U.S. Patent 4,151,190, Apr 24, 1979.
9 Smith, K. J.; Herman, R. G.; Klier, K. Kinetic modelling of higher alcohol
synthesis over alkali-Promoted Cu/ZnO and MoS2 Catalysts. Chem. Eng. Sci.
1990,45,2639-2646.
Li, Z.; Fu, Y.; Bao, J.; Jiang, M.; Hu, T.; Liu, T.; Xie, Y.-N. Effect of
cobalt
promoter on Co-Mo-K/C catalysts used for mixed alcohol synthesis. Appl.
Catal.,
A 2001, 220, 21-30.
11 Woo, H.C.; Park, K. Y. Mixed alcohols synthesis from carbon monoxide and
dihydrogen over potassium-promoted molybdenum carbide catalysts. App!.
Catal., A 1991, 75, 267-280.
12 Te, M.: Lowenthal, E.E.; Foley, H. C. Comparative study of Rh/Al 2O3 and Rh-
Mo/Al 2O3 catalysts. Chem. Eng. Sci. 1994, 49, 4851-4859.
13 Sudhakar, C.; Bhore, N. A.; Bischoff, K. B.; Manogue, W. H.; Mills, G. A.
Molybdena enhanced Rh/Al2O3 catalysts. In Proceedings of the 10th Meeting of
the Catalysis Society of North America, San Diego, CA, 1987.
14 Li, Z.-R.; Fu, Y.-L.; Jiang, M. Structures and performance of Rh-Mo-K/A1203
catalysts used for mixed alcohol synthesis from synthesis gas. Appl. Catal., A
1999, 187, 187-198.
13 Foley, H. C.; Hong, A. J.; Brinen, J. S.; Allard, L. F.; Garratt-Reed, A.
J.
Bimetallic catalysts comprised of dissimilar metals for the reduction of
carbon
monoxide with hydrogen. Appl. Catal., A 1990, 61, 351-375.
16 Shen, J. Y.; Matsuzaki, T.; Hanaoka, T.; Takeuchi, K.; Sugi, Y. The
promoter
function of molybdenum in Rh/Mo/Si02 catalysts for CO hydrogenation. Catal.
Lett. 1994, 28, 329-339.
17 Decanio, E. C.; Storm, D. A. Carbon monoxide adsorption by
CA 02739142 2011-05-05
K/Co/Rh/Mo/A1203 higher alcohols catalysts. J. Catal. 1991, 132, 375-387.
18 Gang, L.; Zhang, C. F.; Chang, Y.; Zhu, Z.; Ni, Y.; Cheng, L.; Yu, F.
Synthesis
of mixed alcohols from C02 contained syngas on supported molybdenum sulfide
catalysts. Appl. Catal., A 1997, 150, 243-252.
19 Qi, H.; Li, D.; Yang, C.; Ma, Y.; Li, W.; Sun, Y.; Zhong, B. Nickel and
manganese co-modified K/MoS2 catalyst: high performance for higher alcohols
synthesis from CO hydrogenation. Catal. Commun. 2003, 4, 339-342.
20 Sun, M.; Nelsona, A. E.; Adjaye, J. On the incorporation of nickel and
cobalt
into M0S2-edge structures. J. Catal. 2004, 226, 32-40.
2' Harris, S.; Chianelli, R. R. Catalysis by transition metal sulfides: A
theoretical
and experimental study of the relation between the synergic systems and the
binary transition metal sulfides. J. Catal. 1986, 98, 17-31.
22 Murchison, C. B.; Murdick, D. A. Process for producing olefins from carbon
monoxide and hydrogen. U.S. Patent 4,199,522, Apr 22, 1980.
23 Tatsumi, T.; Muramatsu, A.; Fukunaga, T.; Tominaga, H. Nickel promoted
molybdenum catalysts for synthesis of mixed alcohols. In Proc. 9th Intern.
Congr.
Catal.; Phillips, M. J., Ternan, M., Eds.; The Chemical Institute of Canada:
Ottawa, 1988; Vol. 2, p 618.
24 Fujumoto, A.; Oba, T. Synthesis of C1-C7 alcohols from synthesis gas with
supported cobalt catalysts. Appl. Catal., A 1985, 13, 289-319.
25 Santiesteban, J. G.; Bogdan, C. E.; Herman, R. G.; Klier, K. Mechanism of
C1-
C4 alcohol synthesis over alkali/M0S2 and alkali/Co/MoS2 catalysts. In Proc.
9th
Intern. Congr. Catal.; Phillips, M. J., Ternan, M., Eds.; The Chemical
Institute of
Canada: Ottawa, 1988; Vol. 2, p 561.
26 Wong, S. F.; Stromville, N. Y.; Storm, D. A.; Montvale, N. J.; Patel, M. S.
Catalyst and method for producing lower aliphatic alcohols. US Patents
4,983,638, Jan 8, 1991.
27 Li, X.; Feng, L.; Zhang, L.; Dadyburjor, D. B.; Kugler, E. L. Alcohol
synthesis
over pre-reduced activated carbon-supported molybdenum-based catalysts.
CA 02739142 2011-05-05
81
Molecules 2003, 8, 13-30.
28 Iranmahboob, J.; Toghiani, H.; Hill, D. 0. Dispersion of alkali on the
surface of
Co-MoS2/clay catalyst: a comparison of K and Cs as a promoter for synthesis of
alcohol. Appl. Catal., A 2003, 247, 207-218.
29 Li, Z.; Jiang, M.; Bian, G.; Fu, Y.; Wei, S. Effect of rhodium modification
on
structures of sulfided Rh-Mo-K/A1203 catalysts studied by XAFS. J. Synch.
Radiat. 1999, 6, 462-464.
30 Kohl, A.; Linsmeier, C.; Taglauer, E.; Knozinger, H. Influence of support
and
promotor on the catalytic activity of RhNO,/SiO2 model catalysts. Phys. Chem.
Chem. Phys. 2001, 3,4639-4643.
31 Wang, Y.; Li, J.; Mi, W. Probing study of Rh catalysts on different
supports in
CO hydrogenation. React. Kinet. Catal. Left. 2002, 76, 141-150.
32 Xua, R.; Yanga, C.; Wei, W.; Li, W.-H.; Suna, Y.-H.; Hu, T.-D. Fe-modified
CuMnZrO2 catalysts for higher alcohols synthesis from syngas. J. Mot. Catal.
A:
Chem. 2004, 221, 51-58.
33 Zurita, M. J. P.; Cifarelli, M.; Cubeiro, M. L.; Goldwasser, J. A. M.;
Pietri, E.;
Garcia, L.; Aboukais, A.; Lamonier, J.-F. Palladium-based catalysts for the
synthesis of alcohols. J. Mol. Catal. A: Chem. 2003, 206, 339-351.
34 Ryndin, Y. A.; Hicks, R. F.; Bell, A. T. Effects of metal-support
interactions on
the synthesis of methanol over palladium. J. Catal. 1981, 70, 287-297.
35 Kogelbauer, A.; Goodwin, J. G.; Oukaci, R. Ruthenium promotion of Co/A1203
Fischer-Tropsch catalysts. J. Catal. 1996, 160, 125-133.
36 Concha, B. E.; Bartholomew, G. L.; Bartholomew, C. H. CO hydrogenation on
supported molybdenum catalysts: Effects of support on specific activities of
reduced and sulfided catalysts. J. Catal. 1984, 89, 536-541.
37 Murchison, C. B.; Conway, M. N.; Steven, R. R.; Quarderer, G. J. Mixed
alcohols from syngas over molybdenum catalysts. In Proceedings of the Ninth
International Congress on Catalyst; 1998; Vol. 2, p 626.
38 Duchet, J. C.; van Oers, E. M.; de Beer, V. H. J.; Prins, R. Carbon
supported
CA 02739142 2011-05-05
82
sulfide catalysts. J. Catal. 1983, 80, 386-402.
39 Zaman, M.; Khodadi, A.; Mortazavi, Y. Fischer-Tropsch synthesis over cobalt
dispersed on carbon nanotubes-based supports and activated carbon. Fuel
Process. Technol. 2009, 90, 1214-1219.
4' Rodriquez-Reinoso, F. The role of carbon materials in heterogeneous
catalysis.
Carbon 1998, 36, 159-175.
4' Eswaramoorthi, I.; Sundaramurthy, V.; Das, N.; Dalai, A. K.; Adjaye, J.
Application of multi-walled carbon nanotubes as efficient support to NiMo
hydrotreating catalyst. Appl. Catal., A 2008, 339, 187-195.
42 Xiaoming, M.; Guodong, L.; Hongbin, Z. Co-Mo-K sulfide-based catalyst
promoted by multiwalled carbon nanotubes for higher alcohol synthesis from
syngas. Chin. J. Catal. 2006, 27, 1019-1027.
43 Surisetty, V. R., Tavasoli, A.; Dalai, A. K. Synthesis of higher alcohols
from
syngas over alkali promoted MoS2 catalysts supported on multi-walled carbon
nanotubes. Appl. Catal. A 2009, 365, 243-251.
44 Moronta, A.; Troconis, M. E.; Gonzalez, E.; Moran, C.; Sanchez, J.;
Gonzalez,
A.; Quinonez, J. Dehydrogenation of ethylbenzene to styrene catalyzed by Co,
Mo and CoMo catalysts supported on natural and aluminum-pillared clays: Effect
of the metal reduction. Appl. Catal., A 2006, 310, 199-204.
41 Jiang, M.; Bian, G.-Z.; Fu, Y.-L. Effect of the K---Mo interaction in K---
MoO3/y-
A1203 catalysts on the properties for alcohol synthesis from syngas. J. Catal.
1994,146,144-154.
46 Calafata, A.; Vivas, F.; Brito, J. L. Effects of phase composition and of
potassium promotion on cobalt molybdate catalysts for the synthesis of
alcohols
from CO2 and H2. Appl. Catal., A 1998, 172, 217-224.
47 Fu, Y.-L.; Fujimoto, K.; Lin, P.; Omata, K.; Yu, Y. Effect of calcination
conditions of the oxidized precursor on the structure of a sulfided K-Mo/y-
AI203
catalyst for mixed alcohol synthesis. Appl. Catal., A 1995, 126, 273-285.
CA 02739142 2011-05-05
83
48 Pan, X.; Fan, Z.; Chen, W.; Ding, Y.; Luo, H.; Bao, X. Enhanced ethanol
production inside carbon-nanotube reactors containing catalytic particles.
Nat.
Mater. 2007, 6, 507-511.
49 Berge, P. J. V.; van de Loosdrecht, J.; Barradas, S.; van der Kraan, A. M.
Oxidation of cobalt based Fischer-Tropsch catalysts as a deactivation
mechanism. Catal. Today 2000, 58, 321-334.
So Feng, L.; Li, X.; Dadyburjor, D. B.; Kugler, E. L. A temperature-programmed-
reduction study on alkali-promoted, carbon-supported molybdenum catalysts. J.
Catal. 2000, 190, 1-13.
51 Noronha, F. B.; Baldanza, M. A. S.; Schmal, M. CO and NO Adsorption on
Alumina-Pd-Mo Catalysts: Effect of the Precursor Salts. J. Catal. 1999, 188,
270-280.
52 Surisetty, V. R.; Dalai, A. K.; Kozinski, J. Synthesis of higher alcohols
from
synthesis gas over Co-promoted alkali-modified MoS2 catalysts supported on
MWCNTs. Appl. Catal., A 2010, in press.
53 Surisetty, V. R.; Dalai, A. K.; Kozinski, J. Effect of Rh promoter on MWCNT-
supported alkali-modified MoS2 catalysts for higher alcohols synthesis from CO
hydrogenation. Appl. Catal. A, 2010, 381, 282-288.
54 Surisetty, V. R.; Dalai, A. K.; Kozinski, J. Alkali-promoted trimetallic Co-
Rh-Mo
sulfide catalysts for higher alcohols synthesis from synthesis gas: Comparison
of
MWCNT and activated carbon supports. Ind. Eng. Chem. Res. 2010, 49, 6956-
6963.
55 Surisetty, V. R.; Dalai, A. K.; Kozinski, J. Intrinsic reaction kinetics of
higher
alcohols synthesis from synthesis gas over sulfided alkali-promoted Co-Rh-Mo
trimetallic catalyst supported on MWCNTs. Energ. Fuel. 2010, in press.
56 Bhusan, B., Ed. Springer handbook of nanotechnology, 2nd ed., Springer:
New York, 2007.
5' Eswaramoorthi, I.; Sundaramurthy, V.; Dalai, A. K. Partial oxidation of
methanol for hydrogen production over carbon nanotubes supported Cu-Zn
CA 02739142 2011-05-05
84
catalysts. Appl. Catal., A 2006, 313, 22-34.
58 Pan, X.; Fan, Z.; Chen, W.; Ding, Y.; Luo, H.; Bao, X. Enhanced ethanol
production inside carbon-nanotube reactors containing catalytic particles.
Nat.
Mater. 2007, 6, 507-511.
59 Berge, P. J. V.; van de Loosdrecht, J.; Barradas, S.; van der Kraan, A. M.
Oxidation of cobalt based Fischer-Tropsch catalysts as a deactivation
mechanism. Catal. Today 2000, 58, 321-334.
60 Kogelbauer, A.; Goodwin, J. G.; Oukaci, R. Ruthenium promotion of Co/AI2O3
Fischer-Tropsch catalysts. J. Catal. 1996, 160, 125-133.
61 Rodriguez, J. A.; Chaturbedi, S.; Hanson, C. J.; Albornoz, A.; Brito, J. L.
Reaction of H2 and H2S with CoMoO4 and NiMoO4: TPR, XANES, Time-resolved
XRD, and molecular-orbital studies. J. Phys. Chem. B 1999, 103, 770-781.
62 Zubavichus, Y. V.; Slovokhotov, Y. L.; Schilling, P. J.; Tittsworth, R. C.;
Golub,
A. S.; Protzenko, G. A.; Novikov, Y. N. X-ray absorption fine structure study
of
the atomic and electronic structure of molybdenum disulfide intercalation
compounds with transition metals. Inorg. Chim. Acta 1998, 280, 211-218.
6; Guay, D.; Divigalpitiya, W. M. R.; Manger, D.; Feng, X. H. Chemical bonding
in restacked single-layer MoS2 by X-ray absorption spectroscopy. Chem. Mater.
1994, 6, 614-619.
64 Hay, S. J.; Metson, J. B.; Hyland, M. M. Sulfur speciation in aluminum
smelting anodes. Ind. Eng. Chem. Res. 2004, 43, 1690-1700.
65 Aritani, H.; Tanaka, T.; Funabiki, T.; Yoshida, S. Study of the local
structure of
molybdenum-magnesium binary oxides by means of Mo L3-edge XANES and
UV-Vis spectroscopy. J. Phys. Chem. 1996, 100, 19495-19501.
66 Topsoe, H.; Clausen, B. S.; Topsoe, N. Y.; Pederson, E. Recent basic
research
in hydrodesulfurization catalysis. Ind. Eng. Chem. Fundam. 1986, 25, 25-36.
67 Rouquerol, J.; Avnir, D; Fairbridge, C. W.; Everett, D. H.;, Haynes, J. H.;
Pernicone, N.; et al. Recommendations for the characterization of porous
solids.
CA 02739142 2011-05-05
Pure App!. Chem. 1994, 66, 1739-1758.
68 Azevedo, D. C. S.; Araujo, J. C. S.; Bastos-Neto, M.; Torres, A. E. B.;
Jaguaribe, E. F.; Cavalcante, C. L. Microporous activated carbon prepared from
coconut shells using chemical activation with zinc chloride. Micropor.
Mesopor.
Mat. 2007, 100, 361-364.
69 Huang, Z.-D.; Bensch, W.; Kienle, L.; Fuentes, S.; Alonso, G.; Ornelas, C.
SBA-1 5 as support for MoS2 and Co-MoS2 catalysts derived from thiomolybdate
complexes in the reaction of HDS of DBT. Catal. Lett. 2008, 122, 57-67.
70 Vradman, L.; Landau, M. V.; Herskowitz, M.; Ezersky, V.; Talianker, M.;
Nikitenko, S.; et al. High loading of short WS2 slabs inside SBA-15: promotion
with nickel and performance in hydrodesulfurization and hydrogenation. J.
Catal.
2003,213,163-175.
71 Kumaran, G. M.; Garg, S.; Soni, K.; Kumar, M.; Sharma, L. D.; Dhar, G. M.;
et
al. Effect of Al-SBA-1 5 support on catalytic functionalities of hydrotreating
catalysts: I. Effect of variation of Si/Al ratio on catalytic functionalities.
App!.
Catal., A 2006, 305, 123-129.
72 Li, Z.-R.; Fu, Y.-L.; Jiang, M.; Hu, T.-D.; Liu, T.; Xie Y.-N. Active
carbon
supported Mo-K catalysts used for alcohol synthesis. J. Catal. 2001, 199, 155-
161.
73 Jiang, M.; Bian, G.-Z.; Fu, Y.-L. Effect of the K---Mo interaction in K---
M003/Y-
A1203 catalysts on the properties for alcohol synthesis from syngas. J. Catal.
1994, 146, 144-154.
74 Calafata, A.; Vivas, F.; Brito, J. L. Effects of phase composition and of
potassium promotion on cobalt molybdate catalysts for the synthesis of
alcohols
from CO2 and H2, Appl. Catal., A 1998, 172, 217-224.
75 Fu, Y.-L.; Fujimoto, K.; Lin, P.; Omata, K.; Yu, Y. Effect of calcination
conditions of the oxidized precursor on the structure of a sulfided K-Mo/y-
A1203
catalyst for mixed alcohol synthesis. App!. Catal., A 1995, 126, 273-285.
CA 02739142 2011-05-05
86
76 Taguchi, G. System of experimental design. Quality Resources, Kraus and
Americans
Supplier Institute (eds): USA, 1991.
77 Bolboaca, S. D.; Jantschi, L. Design of experiments: Useful orthogonal
arrays for number
of experiments from 4 to 16. Entropy 2007, 9, 198-232.
'8 Fogler, H. S. Elements of Chemical Reaction Engineering, Prentice Hall PTR,
USA, 3rd ed., 1999.
79 Butt, J. B. Reaction Kinetics and Reactor Design, USA, 2nd ed., 2000.
80 Frossling N. The evaporation of falling drops. Gerlands Beitr. Geophys.
1938,
52, 170-216.
81 Beretta, A.; Micheli, E.; Tagliabue, L.; Tronconi, E. Development of a
process
for higher alcohol production via synthesis gas. Ind. Eng. Chem. Res. 1998,
37,
3896-3908.
82 Tronconi, E.; Forzatti, P.; Pasquon, I.I. An investigation of the
thermodynamic
constraints in higher alcohol synthesis over Cs-promoted ZnCr-oxide catalyst.
J.
Catal. 1990, 124, 376-390.
83 Tronconi, E.; Ferlazzo, N.; Pasquon, I. Synthesis of alcohols from carbon
oxides and hydrogen. Ind. Eng. Chem. Res. 1987, 26, 2122-2129.
84 Gunturu, A. K.; Kugler, E. L.; Cropley, J. B.; Dadyburjor, D. B. A kinetic
model
for the synthesis of high-molecular-weight alcohols over a sulfided Co-K-Mo/C
catalyst. Ind. Eng. Chem. Res. 1998, 37, 2107-2115.
85 Christensen, J. M.; Mortensen, P. M.; Trane, R.; Jensen, P. A.; Jensen, A.
D.
Effects of H2S and process conditions in the synthesis of mixed alcohols from
syngas over alkali-promoted cobalt-molybdenum sulfide. Appl. Catal. A, 2009,
366, 29-43.
86 Chen, W.; Fan, Z.; Pan, X.; Bao, X. Effect of confinement in carbon
nanotubes
on the activity of Fischer-Tropsch iron Catalyst, J.Am. Chem. Soc, 2008, 130,
9414-9419.
CA 02739142 2011-05-05
87
87 Tavasoli, A.; Tre'panier, M.; Dalai, A. K.; Abatzoglou, N. Effects of
confinement
in carbon nanotubes on the activity, selectivity, and lifetime of Fischer-
Tropsch
Co/carbon nanotube catalysts. J. Chem. Eng. Data 2010, in press.
88 Eswaramoorthi, I.; Sundaramurthy, V.; Das, N.; Dalai, A. K.; Adjaye, J.
Application of multi-walled carbon nanotubes as efficient support to NiMo
hydrotreating catalyst. Appl. Catal. A 2008, 339, 187-195.
89 Li, Z.; Fu, Y.; Jiang, M.; Hu, T.; Liu, T.; Xie, Y. Active carbon supported
Mo-K
catalysts used for alcohol synthesis. J. Catal. 2001, 199, 155-161.
90 Jiang, M.; Bian, G-Z.; Fu, Y-L. Effect of the K---Mo interaction in K---
MoO3/y-
A1203 catalysts on the properties for alcohol synthesis from syngas. J. Catal.
1994,146,144-154.
91 Calafata, A.; Vivas, F.; Brito, J. L.; Effects of phase composition and of
potassium promotion on cobalt molybdate catalysts for the synthesis of
alcohols
from CO2 and H2, Appl. Catal., A 1998, 172, 217-224.
92 Fu, Y-L.; Fujimoto, K.; Lin, P.; Omata, K.; Yu, Y. Effect of calcination
conditions of the oxidized precursor on the structure of a sulfided K-Mo/y-
A1203
catalyst for mixed alcohol synthesis. Appl. Catal. A 1995, 126, 273-285.
93 Vogelaar, B. M.; Steiner, P.; van der Zijden, P. F.; van Langeveld, A. D.;
Eijsbouts, S.; Moulijn, J. A. Catalyst deactivation during thiophene HDS: The
role
of structural sulfur. Appl. Catal., A. 2007, 318, 28-36.
94 Ratnasamy, P.; Sivasanker, S. Structural chemistry of Co-Mo-alumnina
catalysts. Cat. rev. 1980, 22, 401-429.
95 Baghalha, M.; Hoseini, S. M. Long-term deactivation of a commercial CoMo/y-
Al2O3 catalyst in hydrodesulfurization of a naphtha stream. Ind. Eng. Chem.
Res.
2009, 48, 3331-3340.
CA 02739142 2011-05-05
r-
0 N
.E S - LO 00 00 r- co
E N
O
C O co M d' M It
N N ~-
0 =L 0
4)
L d E O) 0) r- O) co N 0)
O O E O oo r
+o L E CD C) CO N
O O v
~.., a 0 ) O O O O O O O
d
C) CO r- co 0) r- M
00 W `~ L `~ ti CO In O) co
co 3 m E N N-
O N r- coO U') c7 lf)
d r
L ,N \ co N co co O)
CL ~:
O O co N- rn
C1 i i d ~t co co
O LU O LU O
= U It Cfl CO
O
W ~ i i LO LU U') LO LU
c r r r r
Lai
LU LU Ln LU
v
a) 0) 0) 0) 0)
cn o 0 U U
vs HU H o HUQ oQ
m cu Z 0 ZU Z
?+
0 \
Z 0 o>'o o>\ o'. 0
CA 02739142 2011-05-05
89
Table 2
Crystal Reflection
phase 20 d-spacing plane
hkl
Oxidized form of catalysts:
Graphite (C) 26.6 3.347 1 1 1
MoO3 40.2 2.271 1 5 0
KM04O6 16.0 5.336 110
K2M02O7 19.4 4.689 110
K2Mo7O20 23.6 3.770 102
K2Mo2O7 28.5 3.222 0 0 2
K2M02O7 29.8 2.956 012
K2Mo2O7 30.9 2.845 2 1 0
KM04O6 37.1 2.403 400
K2Mo7O20 53.8 1.700 0104
Sulfided form of catalysts:
M0S2 14.6 6.110 003
MoS2 33.4 2.707 101
MoS2 40.9 2.199 015
MoS2 58.9 1.570 110
K0.4M0S2 21.5 4.130 004
KM03S3 28.7 3.100 111
K2M0S4 29.9 3.020 30 1
K2M0S4 31.5 2.780 302
Co9S8 52.4 1.751 440
CA 02739142 2011-05-05
} 1 UO (p 14- 00 00 0)
J d' .- ti 00 LC)
= Q N M 04
H I I
0
J o Q J C:)~~ M m
cf) . 0 2N rn 00
-j Lu ca
0 O
a z
~N-mc 0
c0 Un rn 0
w
C N
=
U \
w (DI`O)N-cV -
00 a J d- v- 00 Lc d U
U o
0 c')N,-NN O
w 2
a 0)
-1 0 z
w 0 N~M00~
2 Q
1- O NMNN-N H
U)QH=Q o0000
cõ) U U U M
E
LL
CD O _j O LO I- LC) o
CY) Q Ve Q = r- 't M CO In M
a o 0 Cl) N N N ~ ~ II
F.. JQ 00000
2
0 (D
O ~N0)NCO
V
w z O L 00 =- L 0
Z M M ON
0 M
II
H
Z a_
M
0o II
Oh
c
~~ o o
Z= 2 2 2 N
oc~ o~ 4
U pU o CO
U o U 0
0 N
J U o o
4-
Q 2 to LC) 0
U t(Dto
CA 02739142 2011-05-05
91
Table 4
Sample A B C D
Co-Mo-K/Co Co- Rh-Mo-
Catalyst Co-Mo- Rh-Mo-K/ decorated
K/AC A1203 MWCNTs K/MWCNTs
Temperature (K) 330 327 340 330
H2/CO molar ratio 2.0 2.0 1.0 1.0
Pressure (MPa) 5.0 4.0 5.0 8.3
CO conversion (%) 14.3 4.4 12.6 48.6
STY of alcohols 0.199* 0.062** 0.154 0.261
(g/(g of cat. /h))
CA 02739142 2011-05-05
Ln
N N
CD O CO (00)`*- MCO
LM 0 M000)~N II
V M M M N 0
' C
.1.~ L
0 d o c N CO CO (0 CO
s (o CO Oi LO N E
r- N
4a r-- o w 0
t U
0 0
c
C4 ()NOI-(NN
d 0)000 (.0 C.
2
U
0
N o U') LO N- O CV C0 0
o M Cfl O CO Co O
U 0 0 Nc')(Y)Nco co
E
c (-
O
_.Q E
CY ~CO MNCO N CO
~++FO. OL N M
000000
I I
V .j+ >
O = Co
0 = CD
0. ~ t Nco MOLUO)0
C O U) NNNO'-o
V 0 0 0 0 0 0
Cu CY)
M
I I
F-
.O
i ,.. r0)MNco(0
O Cfl f- - 6
> N It 'q L (.0 M
0
C) aj
I I
F-
z 04
y C) L) 11
U.~Y'~ c0i
O O O
o o-c ~
o o- 0 0 0 '
UI ~/ LUUU -
CA 02739142 2011-05-05
93
Table 6
BET surface Total pore Average
Catalyst area volume pore
(m2/g) (cc/g) diameter
(nm)
Mo-K/MWCNT 109 0.41 14.9
Co-Mo-K/MWCNT 89 0.36 15.7
Rh-Mo-K/MWCNT 86 0.35 16.0
Co-Rh-Mo-K/MWCNT 79 0.29 16.7
Co-Rh-Mo/MWCNT 68 0.23 17.8
Co-Rh-Mo-K/AC 111 0.21 6.4
CA 02739142 2011-05-05
94
Table 7
Reflection
Crystal phase 20 d-spacing plane
hkl
Graphite (C) 26.6 3.35 1 1 1
M0S2 14.6 6.11 0 0 3
M0S2 33.4 2.71 1 0 1
M0S2 40.9 2.20 015
M0S2 58.9 1.57 110
K0.4MoS2 21.50 4.13 004
KM03S3 28.7 3.10 111
K2M0S4 29.9 3.02 3 0 1
K2M0S4 31.5 2.78 3 0 2
Co9S8 52.4 1.75 440
CA 02739142 2011-05-05
e ) OCoa u OO
O It) CO M ~- Q
~~C') N O)
E N CO O O) E 4-.
r r,~ 4M M = O
O N
> N
00 O) 00 N. in O
E O - O If) N Q
> O O O O O O N
0c
cc q- c) c) 0
CD N
y O O O O O
c4 i
V W N- CON C) 00 EO
0 0 0 O O c
N Y
0 N E O
0) 0
O O 0
>
WM
L W
O
mN ~ N
''^^ CO v/ E co cu
0
LO (D 00 r- v-
O _
O) S2 O M ,T r- O) O) IO O
R) 0
N~00 O M 0 In
Q r 'V'
N M m
tt)-M Lo N O O
E M M s- N Lf) `t 4)
0
0 0 0 O
CL > v
CU
a N C
0) c)co f'- M M O V
c. 0) (0 ' M LO c-
> i v 000 c- C) 0EL
N
0 O) tiM - M N i 0
Cl) E rn 0 T) '- E
o 0
m CU
0
w 0 0 0 CO
E CD N ~ co , N
r N ~ ~
V
,C
cts E
m (D Q) .2
X O N LO N
~ 0. 7
O N 0 U)
~' v 'v d. W D
F- a)
>% 0 t x D C~ Z CO
' o
a D~~U U Q
a w a) c
m m c) L) C,3
0U) <<<< vii U)Q c
CA 02739142 2011-05-05
96
Table 9
Total number of metal Dispersion of
Catalyst CO uptake atoms present in the metals
support (pmole/g of cat.) sample (%)
(pmole/g of cat.)
AC-Darco 137 495 27.7
AC-RX3 extra 140 495 28.3
AC-Fluid coke 161 495 32.6
AC-CGP 195 495 39.4
super
MWCNT 237 495 47.9
CA 02739142 2011-05-05
i v)
t t ti es r= 00
O)O ANN M CON
+~'+ = V r~-r r r II
=~ t4 0
V 1
O ca
O O
cr) I-
M co E
O 3 - 00 co 0)
c W O
TN
Q O T
Nf- M Nt 00
t co M I-
m Co
U
O
0)
V d ~
~N co CO O
O O E N cc) N N (o U-) C6 N a_
i ._. U)
Q.
O
E
O C I;t r- CO LO U-) ro
O i O O LO
m N N N co M
~'~,= 1- 000 O 611
v >
y) _
O N- N CO
O LC) 00 O O)
IL v o -7 N N U
0
-- F- IL) C) C) c:) O o0
M
M
I I
O Co
O =0) ~. CO CO 00 LC) c}'
V> ~.. M M d LC) M
co
0
C) I I
3-
03)
Y N
X U II
O O -a I- Rf
L) cl) Z v
a OoIiU aOQ)
C.
u~i~ p
U vii QQQ Q
CA 02739142 2011-05-05
98
Table 11
Model Quality of fit (R2 Value)
Methanol STY 0.993
(Ethanol STY) 0.5 0.981
(Higher alcohols STY)0'5 0.980
(Total alcohols STY) 0.5 0.982
Hydrocarbons STY 0.971
CO2 STY 0.954
(Methanol selectivity)0.5 0.987
(Ethanol selectivity)0'5 0.975
Higher alcohols 0.943
selectivity
Total alcohols selectivity 0.860
CA 02739142 2011-05-05
D to
GD o >O0)'
0 0 0 CO CO I-
V O O O
d N
i
0
N
GW 0 > CO CO C0
Ctt= 4 Nfl-
V O)OCO
V= V O O O O
C Cl)
C o
N
a) a (D C3) LO
W O O O
O ... O
E
O O
C +
ao O
t4 >
0 0 0
N
0
m C -~
.v
G)
0 o-OO C <a_
CA 02739142 2011-05-05
100
Table 13
H2/CO 1 1.5 2
(moles/moles)
Repetitions # 4 3* 3*
Ethanol STY 0.148, 0.150, 0.126, 0.128, 0.116, 0.114,
(g/(g of cat.)/h) 0.151, 0.154 0.124 0.115
Ethanol 25.8, 26.1, 26.6, 19.5, 20.1, 19.1 9.6, 9.1, 9.6
selectivity (wt %) 25.7
Repetitions # 2~* 22
Ethanol STY 0.151, 0.152 0.122, 0.127 0.113, 0.119
(g/(g of cat.)/h)
Ethanol 26.5, 26.7 18.8, 19.7 9.5, 10.2
selectivity (wt %)
t - value
Ethanol STY 0.39 0.29 0.42
(g/(g of cat.)/h)
Ethanol 1.78 0.63 1.23
selectivity (wt %)
p - value
Ethanol STY 0.358 0.287 0.351
(g/(g of cat.)/h)
Ethanol 0.075 0.287 0.153
selectivity (wt %)
(T= 330 C, P = 1320 psig (9.1 Mpa), and GHSV = 3.8 m3 (STP)/(kg of cat./h))
experiments were repeated using same catalyst; **experiments were repeated
using freshly loaded catalyst every time
CA 02739142 2011-05-05
101
Table 14
Run T P GHSV H2/CO
( C) (psi) (m3 (STP)/(kg of cat.)/h) (moles/moles)
Set-1
14 350 1000 3.6 0.5
13 350 800 4.2 1.0
1 275 800 2.4 0.5
11 325 1200 2.4 1.0
15 350 1200 3.0 2.0
2 275 1000 3.0 1.0
12 325 1400 3.0 0.5
300 800 3.0 1.5
8 300 1400 3.6 1.0
4 275 1400 4.2 2.0
9 325 800 3.6 2.0
6 300 100 2.4 2.0
3 275 1200 3.6 1.5
325 1000 4.2 1.5
7 300 1200 4.2 0.5
16 350 1400 2.4 1.5
CP 315 1100 3.3 1.25
Set - 2
1 320 1200 3.6 1.25
3 320 1400 4.0 1.25
5 330 1300 4.0 1.25
4 330 1200 3.8 1.25
6 330 1400 3.6 1.25
7 340 1200 4.0 1.25
8 340 1300 3.6 1.25
2 320 1300 3.8 1.25
9 320 1400 3.8 1.25
CA 02739142 2011-05-05
O M ~- ~- N
L C
N M N
~=y r r r
N O
E O O O M
O tt
V r
U,
V-
. 4.+
m
O O LU LO LU
2
O
EY rn rn rn rn
0
0
a)
C
0)
N_
N
O Imo- O
m T--
0 C) 0 N N
00
C E O N O I`
a v r- d' N
CA 02739142 2011-05-05
103
Table 16
Particle size range (pm) dp (mm) k (m/s) b (mm)
T = 275 C
707-841 0.774 3.62 * 10-4 0.142
420-500 0.460 5.21 * 10-4 0.099
210-297 0.254 8.06 * 10-4 0.064
147-210 0.179 1.05 * 10-4 0.049
T = 300 C
707-841 0.774 3.65 * 10 0.144
420-500 0.460 5.25 * 10-4 0.100
210-297 0.254 8.13 * 10-4 0.065
147-210 0.179 1.06 * 10-4 0.049
T = 325 C
707-841 0.774 3.69 * 10 0.146
420-500 0.460 5.32 * 10-4 0.101
210-297 0.254 8.24 * 10-4 0.065
147-210 0.179 1.08 * 10-4 0.050
T = 350 C
707-841 0.774 3.72 * 10 0.147
420-500 0.460 5.37 * 10-4 0.102
210-297 0.254 8.34 * 10"4 0.066
147-210 0.179 1.09 * 10-4 0.050
(wt. of the cat. = 2 g, P = 9.1 MPa, Flow rate = 120 ml/min, H2/CO molar ratio
=
1.25)
CA 02739142 2011-05-05
O)
ti
T7
O
I I
a)
N
a)
f
Co
0
a)
cv
i
a)
Co
LU
N
T--
11
0
Co cD 00
~f)LULUct _ CO
E 0 0 0 0 E
O O q c,4 q co 0
O O
O O O O
O E
O O O U
N
ti
O co M co
0 0 0 0
r r r S
E IT I? I? C?
k is is O O O O C)
SOON ^ ~- r T- T- N
r N
0 0c)
0) T- - E
O C) O 00
O
E E a-
E E U
0
L i M
I I
0 0 0 O O O H
OONIt O O N It
LL O ' LL Co T- T- 01
N
11
CO
0
a)
L
0
CA 02739142 2011-05-05
105
Table 18
Parameter Value
kcH,oH 1.502 * 10-4
k
('2H 5011 3.511 * 10"2
k HA 1.837 * 103
kHC 3.270 *104
k(.o, 2.928 * 102
E(,H,oH 57
EHA 94
EHC_ 112
Eco, 103
a 0.871
b 1.898
c 0.765
d 1.237
e 0.356
f 1.023
g 0.124
h 1.132
1.118
0.012
k 1.232
0.234
k units depend on the kinetic expression obtained for the corresponding
r;which
is expressed as mole/(kg of cat.)/h; units of E, are in kJ/mole.
CA 02739142 2011-05-05
N
H
Z O
In
O O LU r-- q
O N II M LU 0)
LU 0
L
IY II =
n
U
co C7
(/) 0 O
0
II O "LU
2 (N 0 (o o6
00 CID
U II U
^
LL
L O
~- U ca (N
o w Lf)
m c:) II 00 O
O Q7 r
U II U
N
I
0
O
0 -0
a"Uo 11 CY) (0 'o
-,C)0
.2 II U
ai
(n
0 Un
L C
d
_ +r 0 0 (0 (6
C CD 0
a Co U 0
W 2 2
CA 02739142 2011-05-05
0
411- U)
0 00 f-- 1,- 00
ti d I- L()
N
r.i
ti r
r O v I N N co I-
C.E
3 Z O
i N d-
Q E C E I- CD I,- ti O 00
Q 'Q
_ d
E N N N
7
F.O. Q 0 U O O 0 O O O
w (a C) _
O (0 0) ti O) 00
C)
N
O N O aD 'IT O 'C O ch ' M
c d .-
C N () 00 , O
O O
N M
0 O M co
c) a q 'IT M i M
O L() LU LU LU U) LO
o s U) LO U) LU L[) Ln
G> o - r r r r
O O \
O Ln LU LO LU U) L()
~ r ~ r r r r
O
()
Y O O O) O O) 0)
_0
O N O 0)
Q Q O O -tf
y Q N Q Q U) 0.
U) m N m
w r.+ >+ >, 4-
Ln N N Ln
V ~Z OZ 2Z 2 o
co m m m
U V V U U U
Uacid M Q i 2- Q ~Q
o-co-c
LL0U)0U)oIL00)00)o
CA 02739142 2011-05-05
108
Table 21
Crystal Reflection
phase 20 d-spacing plane
h k I
Graphite (C) 26.6 3.347 1 1 1
MoO3 40.7 2.271 1 5 0
KMo4O6 15.8 5.336 110
K2Mo7O20 23.6 3.770 1 0 2
K2Mo2O7 28.5 3.222 002
KMo4O6 37.10 2.403 400
MoS2 14.6 6.110 003
MoS2 33.4 2.707 101
MoS2 40.9 2.199 015
MoS2 58.9 1.570 110
MoS2 60.0 1.541 003
K0,4MoS2 21.5 4.130 004
KM03S3 28.7 3.100 111
K2M0S4 29.9 3.020 30 1
K2MoS4 31.1 2.780 302
Co9S$ 47.9 1.911 511
Co9S8 52.4 1.751 440
