Note: Descriptions are shown in the official language in which they were submitted.
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1
CATALYST WITH IMPROVED HYDROTHERMAL STABILITY
TECHNICAL FIELD
[0001] The present invention is directed to an exhaust gas purifying
catalyst and methods
.. for its use. More particularly, the invention pertains to catalysts that
arc resistant to thermal
aging and methods of using the materials. The exhaust gas purifying catalyst
may be used to
treat exhaust gas streams, especially those emanating from lean burn engines.
BACKGROUND
[0002] Operation of lean burn engines, for example, diesel engines and lean
bum gasoline
engines, provide the user with excellent fuel economy and have low emissions
of gas phase
hydrocarbons and carbon monoxide due to their operation at high air/fuel
ratios under fuel lean
conditions. Additionally, diesel engines offer significant advantages over
gasoline (spark
ignition) engines in terms of their fuel economy, durability, and their
ability to generate high
torque at low speed.
[0003] From the standpoint of emissions, however, diesel engines present
more severe
problems than their spark-ignition counterparts. Because diesel engine exhaust
gas is a
heterogeneous mixture, emission problems relate to particulate matter (PM),
nitrogen oxides
(NOR), unburned hydrocarbons (HC), and carbon monoxide (CO).
[0004] Emission of nitrogen oxides (NOR) from lean burn engines must be
reduced in order
to meet emission regulation standards. Conventional three-way conversion (TWC)
automotive
catalysts are suitable for abating NOR, carbon monoxide a (CO) and hydrocarbon
(HC)
pollutants in the exhaust of engines operated at or near stoichiometric
air/fuel conditions. The
precise proportion of air to fuel which results in stoichiometric conditions
varies with the
relative proportions of carbon and hydrogen in the fuel. An air-to-fuel (A/F)
ratio of 14.65:1
(weight of air to weight of fuel) is the stoichiometric ratio corresponding to
the combustion of
a hydrocarbon fuel, such as gasoline, with an average formula CH1.88. The
symbol X is thus
used to represent the result of dividing a particular A/F ratio by the
stoichiometric A/F ratio for
a given fuel, so that; X=1 is a stoichiometric mixture, X>1 is a fuel-lean
mixture and X,.<1 is a
.. fuel-rich mixture.
[0005] Engines, especially gasoline-fueled engines to be used for
passenger automobiles
and the like, are being designed to operate under lean conditions as a fuel
economy measure.
2
Such future engines are referred to as "lean burn engines." That is, the ratio
of air to fuel in
the combustion mixtures supplied to such engines is maintained above the
stoichiometric
ratio so that the resulting exhaust gases are "lean," i.e., the exhaust gases
are relatively high
in oxygen content. Although lean-burn engines provide advanced fuel economy,
they have
the disadvantage that conventional TWC catalysts are not effective for
reducing NO.
emissions from such engines because of excessive oxygen in the exhaust.
Attempts to
overcome this problem have included the use of a NO. trap. The exhaust of such
engines is
treated with a catalyst/NOr sorbent which stores NO. during periods of lean
(oxygen-rich)
operation, and releases the stored NO. during the rich (fuel-rich) periods of
operation.
During periods of rich (or stoichiometric) operation, the catalyst component
of the
catalyst/NO. sorbent promotes the reduction of NO. to nitrogen by reaction of
NO.
(including NO. released from the NO sorbent) with HC, CO, and/or hydrogen
present in the
exhaust.
[0006] In a reducing environment, a lean NO. trap (LNT) activates
reactions by
promoting a steam reforming reaction of hydrocarbons and a water gas shift
(WGS) reaction
to provide H2 as a reductant to abate NOR. The water gas shift reaction is a
chemical reaction
in which carbon monoxide reacts with water vapor to form carbon dioxide and
hydrogen.
The presence of ceria in an LNT catalyzes the WGS reaction, improving the LNTs
resistance
to SO2 deactivation and stabilizing the PGM; ceria in an LNT also functions as
a NO. storage
component.
[0007] NO, storage materials comprising barium (BaCO3) fixed to ceria
(Ce02) have
been reported, and these NO. materials have exhibited improved thermal aging
properties.
Ceria, however, suffers from severe sintering upon hydrothermal aging at high
temperatures.
The sintering not only causes a decrease in low temperature NO. storage
capacity and WGS
activity, but also results in the encapsulation of BaCO3 and PGM by the bulk
Ce02. Thus,
there is a need for a ceria-containing catalyst that is hydrothermally stable.
SUMMARY
[0008] Embodiments of a first aspect of the invention are directed to a
catalyst. In a first
embodiment, the catalyst comprises ceria-alumina composite particles having a
ceria phase
present in a weight percent of the composite in the range of 20 % to 80% on an
oxide basis,
an alkaline earth metal component comprising a barium component supported on
the ceria-
alumina composite particles and present in an amount in the range of 5.0 to
30% by weight
on an oxide basis, wherein the Ce02 is present in the form of crystallites
that are
hydrothermally stable
Date Regue/Date Received 2022-11-08
3
and have an average crystallite size as determined by XRD of less than 160A
after aging at
950 C for 5 hours in 2% 02 and 10% steam in N2
[0009] In a second embodiment, the catalyst of the first embodiment is
modified, wherein
the barium component is selected from the group consisting of barium oxide and
barium
carbonate.
[0010] In a third embodiment, the catalyst of the first through second
embodiments is
modified, wherein the ceria-alumina particles are a composite of ceria and
alumina.
[0011] In a fourth embodiment, the catalyst of the third embodiment is
modified, wherein
the composite of Ce02 and A1203 contains ceria in an amount in the range of
about 30 to 80%
by weight on an oxide basis.
[0012] In a fifth embodiment, the catalyst of the third embodiment is
modified, wherein
the composite of Ce02 and A1203 contains ceria in an amount in the range of
about 50 to 80%
by weight on an oxide basis.
[0013] In a sixth embodiment, the catalyst of the first through fifth
embodiments further
comprising at least one platinum group metal selected from the group
consisting of platinum,
palladium, rhodium, iridium, and mixtures thereof, supported on the ceria-
alumina particles.
[0014] In a seventh embodiment, the catalyst of the sixth embodiment is
modified,
wherein the platinum group metal is selected from platinum, palladium,
rhodium, and
mixtures thereof.
[0015] In a eighth embodiment, the catalyst of the sixth through seventh
embodiments is
modified, wherein the platinum group metal consists essentially of platinum
and palladium.
[0016] In the ninth embodiment, the catalyst of the sixth through seventh
embodiments is
modified, wherein the platinum group metal consists essentially of platinum.
[0017] In the tenth embodiment, the catalyst of the first through ninth
embodiments is
modified, wherein the barium component is present in an amount in the range of
about 0.5%
to 50% by weight on an oxide basis.
[0018] In an eleventh embodiment, the catalyst of the first through tenth
embodiments is
modified, wherein the barium component is present in an amount in the range of
about 5% to
30% by weight on an oxide basis.
[0019] In a twelfth embodiment, the catalyst of the first through eleventh
embodiments is
modified, wherein the catalyst is selected from a three-way catalyst (TWC),
diesel oxidation
catalyst (DOC), gasoline particulate filter (GPF), lean NO,, trap (LNT),
integrated lean NOx
trap-three way catalyst (LNT-TWC), or ammonia oxidation (AMOX).
Date Recue/Date Received 2022-05-20
4
[0020] A second aspect of the present invention is directed to a system.
In a thirteenth
embodiment, a system comprises the catalyst of the first through twelfth
embodiments and a
lean burn engine upstream from the catalyst.
[0021] In a fourteenth embodiment, the system of the thirteenth
embodiment is modified,
further comprising a second catalyst and,
[0022] In a fifteenth embodiment, the system of the thirteenth through
fourteenth
embodiments is modified further comprising a particulate filter.
[0023] In a sixteenth embodiment, the system of the fourteenth through
fifteenth
embodiments is modified, wherein the second catalyst is selected from a three-
way catalyst
(TWC), gasoline particulate filter (GPF), selective catalytic reduction (SCR),
lean NO,, trap
(LNT), ammonia oxidation (AMOX), SCR on a filter (SCRoF), and combinations
thereof,
and combinations thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a perspective view of a honeycomb-type refractory
substrate member
which may comprise a washcoat composition comprising the catalyst according to
an
embodiment;
[0025] FIG. 2 is a partial cross-sectional view enlarged relative to FIG.
1 and taken along
a plane parallel to the end faces of the substrate of FIG. 1, which shows an
enlarged view of
one of the gas flow passages shown in FIG. 1;
[0026] FIG. 3 is a graph of crystallite size of the Ce02 as measured by
XRD according to
the Examples in fresh and after aging at 950 C for 5 hours in 2% 02 and 10%
steam in N2,
and
[0027] FIG. 4 is a graph of crystallite size of the Ce02 as measured by
XRD according to
the Examples after aging at 850 C for 8 hours in 10% steam /air.
DETAILED DESCRIPTION
[0028] Before describing several exemplary embodiments of the invention,
it is to be
understood that the invention is not limited to the details of construction or
process steps set
forth in the following description. The invention is capable of other
embodiments and of
being practiced or being carried out in various ways.
Date Recue/Date Received 2022-05-20
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[0029]
According to embodiments of the invention, it has been discovered that
incorporating a barium component (e.g. BaCO3 and/or BaO) into ceria-alumina
(Ce02/A1203)
has a tremendous stabilization effect on Ce02 and, thus, provides a catalyst
material with
improved hydrothermal stability, higher NO,, trapping capacity, and higher
NO,, conversion
5 than traditional technologies.
[0030] In
one or more embodiments, a catalyst comprises ceria-alumina particles having a
ceria phase present in a weight percent of the composite in the range of about
20% to about
80% on an oxide basis, and an alkaline earth metal component supported on the
ceria-alumina
particles. The average Ce02 crystallite size of the fresh and aged samples,
obtained from
XRD, can be used as a measurement for Ce02 hydrothermal stability.
Accordingly, in one or
more embodiments, the Ce02 is present in the form of crystallites that are
hydrothermally
stable and have an average crystallite size of less than 160 A after aging at
950 C for 5 hours
in 2% 02 and 10% steam in N2.
[0031]
With respect to the terms used in this disclosure, the following definitions
are
provided.
100321 As
used herein, the terms "catalyst" or "catalyst material" or "catalytic
material"
refer to a material that promotes a reaction.
[0033] As
used herein, the terms "layer" and "layered" refer to a structure that is
supported
on a surface, e.g. a substrate. In one or more embodiments, the catalyst of
the present
invention is coated as a washcoat on a substrate or substrate member, to form
a layer on a
substrate.
[0034] As used herein, the tei _______________________________________
tit "washcoat" has its usual meaning in the art of a thin,
adherent coating of a catalytic or other material applied to a carrier
substrate material, such as a
honeycomb-type carrier member, which is sufficiently porous to permit the
passage of the gas
stream being treated. As is understood in the art, a washcoat is obtained from
a dispersion of
particles in slurry, which is applied to a substrate, dried and calcined to
provide the porous
washcoat.
[0035] As
used herein, the term "support" refers to the underlying high surface area
material upon which additional chemical compounds or elements are carried. The
support
particles have pores larger than 20 A and a wide pore distribution. As defined
herein, such
metal oxide supports exclude molecular sieves, specifically, zeolites. In
particular
embodiments, high surface area refractory metal oxide supports can be
utilized, e.g., alumina
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support materials, also referred to as "gamma alumina" or "activated alumina,"
which typically
exhibit a BET surface area in excess of 60 square meters per gram ("m2/g"),
often up to about
200 m2/g or higher. Such activated alumina is usually a mixture of the gamma
and delta
phases of alumina, but may also contain substantial amounts of eta, kappa, and
theta alumina
phases. Refractory metal oxides other than activated alumina can be used as a
support for at
least some of the catalytic components in a given catalyst. For example, bulk
ceria, zirconia,
alpha alumina, silica, titania, and other materials are known for such use.
[0036] In
one or more embodiments, the catalyst comprises ceria-alumina particles. The
ceria-alumina particles have a ceria phase present in a weight percent of the
catalyst in the
range of about 20% to about 80% on an oxide basis, including 20%, 25%, 30%,
35%, 40%,
45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%. In one or more specific embodiment,
the
average Ce02 crystallite size of the fresh and aged samples, obtained from
XRD, can be used
as a measurement for Ce02 hydrothermal stability. Accordingly, in one or more
embodiments,
the Ce02 is present in the form of crystallites that are hydrothermally stable
and have an
average crystallite size of less than 160 A, including 160, 155, 150, 140,
130, 120, 110, 10.0,
90, 80, 70, 60, 50, 40, 30, 20, 10, and 5 A, after aging at 950 C for 5 hours
in 2% 02 and 10%
steam in N2. In a specific embodiment, the ceria-alumina particles include a
ceria phase
present in a weight percent of the composite in an amount of about 30% to 80%
by weight on
an oxide basis. In a very specific embodiment, the ccria-alumina particles
include a ceria
phase present in a weight percent of the composite in an amount of about 50%
to 80% by
weight on an oxide basis.
[0037] In
one or more embodiments, the Ce02 is present in the form of crystallites that
are hydrothermally stable and are resistant to growth into larger crystallites
upon aging at 950
C. As used herein, the term "resistant to growth" means that the crystallites
upon aging grow
to a size no larger than an average of 160 A. In a specific embodiment, the
Ce02 crystallite
size, as determined by XRD, after aging the catalytic article at 950 C for 5
hours in 2% 02 and
10% steam/N2 is less than 160 A. According to one or more embodiments, the
Ce02 crystallite
size of the powder samples and the coated catalysts are different. In the
coated catalysts, other
washcoat components may have a stabilization effect on Ce02. Therefore, after
the same 950
C aging, the Ce02 crystallite size of the coated catalyst is smaller than that
of the powder.
[0038] As
used herein, the term "average crystallite size" refers to the mean size as
determined by XRD described below.
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[0039] As used herein, the term "XRD" refers to x-ray diffraction
crystallography, which is
a method of determining the atomic and molecular structure of a crystal. In
XRD, the
crystalline atoms cause a beam of x-rays to diffract into many specific
directions. By
measuring the angles and intensities of these diffracted beams, a three-
dimensional image of
the density of electrons within the crystal can be produced. From this
electron density, the
position of the atoms in the crystal can be determined, as well as their
chemical bonds, their
disorder, and other information. In particular, XRD can be used to estimate
crystallite size; the
peak width is inversely proportional to crystallite size; as the crystallite
size gets smaller, the
peak gets broader. In one or more embodiments, XRD is used to measure the
average
crystallite size of the Ce02 particles.
[0040] The width of an XRD peak is interpreted as a combination of
broadening effects
related to both size and strain. The formulas used to determine both are given
below. The first
equation below is the Scherrer equation which is used to transform full width
at half maximum
intensity, FWHM, information into a crystallite size for a given phase. The
second equation is
used to calculate strain in a crystal from peak width information and the
total width or breadth
of a peak considered to be a sum of these two effects as shown in the third
equation. It should
be noticed that size and strain broadening vary in different fashions with
regard to the Bragg
angle 0. The constants for the Scherrer equation are discussed below.
KA
13L = ____________________________________
L cos9
Pe = CE tane
KA.
13tot = 13e + 13L = CE tan0 + ____________________
L cos0
[0041] The constants for the Scherrer equation are
[0042] K: shape constant, we use a value of 0.9
[0043] L: the peak width, this is corrected for the contribution from the
instrumental optics
through the use of NEST SRM 660b LaB6 Line Position & Line Shape Standard
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[0044] 0: 1/2 of the 20 value of the reflection of interest
[0045] X: wavelength of radiation 1.5406A
[0046] As used herein, "crystallite size" is understood to be the length
of the coherent
scattering domain in a direction orthogonal to the set of lattice planes which
give rise to the
reflection. For Ce02, the CeO2 <111> reflection is the most intense peak in
the X-ray
diffraction pattem of Ce02. The Ce02 <111> plane of atoms intersects each of
the
crystallographic axes at unity and is orthogonal to the body diagonal
represented by the <111>
vector. So, a crystallite size of 312A calculated from the FWHM of the Ce02
111 reflection
would be considered to be roughly 100 layers of the <111> plane of atoms.
[0047] Different directions, and thus reflections, in a crystal will
generate different though
close crystallite size values. The values will be exact only if the crystal is
a perfect sphere. A
Williamson Hall plot is used to interpret size and strain effects by
considering the total peak
breadth as a linear equation below with the slope of the line representing
strain and the
intercept being the size of a crystal.
KX
Not cost) = Cg sin0 +
[0048] To determine the crystallite size of a material FWHM value of a
single reflection or
from the complete X-ray diffraction pattern is determined. Traditionally a
single reflection has
been fit to determine the FWHM value of that reflection, corrected the FWHM
value for the
contribution from the instrument, and then converted the corrected FWHM value
into a
crystallite size value using the Scherrer equation. This would be done by
ignoring any effect
from strain in the crystal. This method has been used primarily for questions
concerning the
crystallite size of precious metals for which we have only a single useful
reflection. It should
be noted that in fitting peaks it is desired to have a clean reflection which
is not overlapped by
reflections from other phases. This is rarely the case with present washcoat
formulations
Rietveld methods are now used. Rietveld methods allow the fit of complex X-ray
diffraction
patterns using the known crystal structures of the phases present. The crystal
structures act as
restraints or brakes on the fitting process. Phase content, lattice
parameters, and FWHM
info' __ illation are varied for each phase until the overall model matches
the experimental data.
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[0049] In the Examples below, Rietveld methods were used to fit
experimental patterns for
fresh and aged samples. A FWHM curve determined for each phase in each sample
was used
to determine a crystallite size. Strain effects were excluded.
[0050] As used herein, the term "alkaline earth metal" refers to one or
more chemical
elements defined in the Periodic Table of Elements, including beryllium (Be),
magnesium
(Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). In one or
more
embodiments, the alkaline earth metal component can be incorporated into the
catalyst as a salt
and/or sulfate and/or oxide (e.g., BaCO3, BaSO4, and/or BaO) to provide an
"alkaline earth
metal component". It is noted that upon calcination, the barium component will
convert to
barium carbonate and/or barium oxide. In one or more embodiments, the alkaline
earth metal
component comprises a barium component. The alkaline earth metal component can
be
present in the washcoat in an amount in the range of about 0.5% to 50% by
weight on an oxide
basis, including 0.5, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, and 50%.
In a specific
embodiment, the alkaline earth metal component comprises a barium component,
which is
present in an amount in the range of about 0.5% to about 50% by weight on an
oxide basis. In
other specific embodiments, the alkaline earth metal component comprises a
barium
component, which is present in an amount in the range of about 5% to about 30%
by weight on
an oxide basis.
[0051] In one or more embodiments, the Ce02 crystallite size of the aged
.samples,
obtained from XRD, was used as a measurement for alkaline carth/Ce/Al
hydrothermal
stability.
[0052] In specific embodiments, a tremendous stabilization effect is
observed when the
ceria-alumina particles are impregnated with barium precursors, particularly
water-soluble
barium precursor salts (e.g. barium acetate), which are calcined to provide
barium carbonate
(BaCO3) and/or barium oxide (Ba0). Referring to FIG. 3, after aging at 950 C
for 5 hours in
2% 02 and 10% steam in N2, the Ce02 crystallite sizes of the BaCO3/(Ce02-
A1203) samples
were within about 75 to about 160 A. This is remarkably lower than that of
aged BaCO3/Ce02
powder (>1000 A). Alternative BaCO3 loadings were applied on 70% Ce02/A1203
powder to
determine if they can also provide a similar effect. Referring to FIG. 4,
after aging at 850 C
for 8 hr in 10% steam/air, the samples loaded with 15, 10, and 5 wt% barium
component
(calculated as barium oxide) show much lower Ce02 crystallite size than the
BaCO3/Ce02.
Overall, it appears that the barium component (e.g. BaCO3 and/or BaO) has a
unique
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stabilization effect on ceria crystallite growth in a Ba/Ce/A1 system. This
stabilization effect is
likely beneficial, for example, for NO, trapping in LNT catalysts. The
additional ceria surface
area resulting from smaller crystallite sizes will allow for more low
temperature ceria based
NO, trapping, improve WGS, and improve PGM dispersion.
5 [0053] Thus, according to one or morc embodiments, the ceria is
destabilized in a Ba-Ce
system, and is significantly stabilized in a Ba-Cc-Al system.
[0054] In one or more embodiments, without intending to be bound by
theory, it is thought
that the additional ceria surface area resulting from smaller crystallite
sizes allows for higher
BaCO3 based NO trapping due to better BaCO3 dispersing, higher Ce02 based NO
trapping at
10 low temperature, improved NO, reduction due to more efficient WGS, and
improved NO
oxidation and NO, reduction due to better PGM dispersion. Thus, incorporating
barium
(BaCO3 and/or BaO) into ceria-alumina (Ce02/A1203) has a tremendous
stabilization effect on
Ce02 and provides a catalyst material with improved hydrothermal stability,
higher NOx
trapping capacity, and higher NO, conversion than traditional technologies.
[0055] In one or more embodiments, the catalyst of the present invention
exhibits
improved NO, trapping capacity during lean operation and improved NO,
reduction during
rich regeneration, after aging at 950 C for 5 hours in 2% 02 and 10%
steam/N2. The
improvement is over traditional catalysts that comprise ceria not incorporated
with Al2O3.
[0056] In one or more embodiments, the catalyst of the invention can be
utilized as a three-
way catalyst (TWC), a diesel oxidation catalyst (DOC), a gasoline particulate
filter (GPF), a
lean NO, trap (LNT), an integrated LNT-TWC, or as an ammonia oxidation
catalyst (AM0x).
[0057] In one or more embodiments, the catalyst further comprises at
least one platinum
group metal supported on the barium(ceria-alumina) particles. As used herein,
the teun
"platinum group metal" or "PGM" refers to one or more chemical elements
defined in the
Periodic Table of Elements, including platinum, palladium, rhodium, osmium,
iridium, and
ruthenium, and mixtures thereof. In one or more embodiments, the platinum
group metal is
selected from the group consisting of platinum, palladium, rhodium, iridium,
and mixtures
thereof In a specific embodiment, the platinum group metal is selected from
platinum,
palladium, rhodium, and mixtures thereof. Generally, there are no specific
restrictions as far as
the total platinum group metal content of the catalyst is concerned.
[0058] Typically, the catalyst of the present invention is disposed on a
substrate. The
substrate may be any of those materials typically used for preparing
catalysts, and will
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typically comprise a ceramic or metal honeycomb structure. Any suitable
substrate may be
employed, such as a monolithic substrate of the type having fine, parallel gas
flow passages
extending therethrough from an inlet or an outlet face of the substrate, such
that passages are
open to fluid flow therethrough (referred to herein as flow-through
substrates). The passages,
which arc essentially straight paths from their fluid inlet to their fluid
outlet, arc defined by
walls on which the catalytic material is coated as a washcoat so that the
gases flowing through
the passages contact the catalytic material. The flow passages of the
monolithic substrate are
thin-walled channels, which can be of any suitable cross-sectional shape and
size such as
trapezoidal, rectangular, square, sinusoidal, hexagonal, oval, circular, etc.
[0059] Such monolithic substrates may contain up to about 900 or more flow
passages (or
"cells") per square inch of cross section, although far fewer may be used. For
example, the
substrate may have from about 7 to 600, more usually from about 100 to 400,
cells per square
inch ("cpsi"). The cells can have cross sections that are rectangular, square,
circular, oval,
triangular, hexagonal, or are of other polygonal shapes. The ceramic substrate
may be made of
any suitable refractory material, e.g., cordierite, cordierite-alumina,
silicon nitride, or silicon
carbide, or the substrates may be composed of one or more metals or metal
alloys.
[0060] The catalyst according to embodiments of the present invention can
be applied to
the substrate surfaces by any known means in the art. For example, the
catalyst washcoat can
be applied by spray coating, powder coating, or brushing or dipping a surface
into the catalyst
composition.
[0061] In one or more embodiments, the catalyst is disposed on a
honeycomb substrate.
[0062] When applied as a washcoat, the invention may be more readily
appreciated by
reference to FIGS. 1 and 2. FIGS. 1 and 2 show a refractory substrate member
2, in
accordance with one embodiment of the present invention. Referring to FIG. 1,
the refractory
substrate member 2 is a cylindrical shape having a cylindrical outer surface
4, an upstream end
face 6 and a downstream end face 8, which is identical to end face 6.
Substrate member 2 has
a plurality of fine, parallel gas flow passages 10 formed therein. As seen in
FIG. 2 flow
passages 10 are formed by walls 12 and extend through substrate from upstream
end face 6 to
downstream end face 8, the passages 10 being unobstructed so as to permit the
flow of a fluid,
e.g., a gas stream, longitudinally through substrate via gas flow passages 10
thereof. A
discrete catalyst layer 14, which in the art and sometimes below is referred
to as a "washcoat",
is adhered or coated onto the walls 12 of the substrate member. In some
embodiments, an
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additional catalyst layer 16 is coated on top of the catalyst layer 14. The
second catalyst layer
16 can be the same composition as the catalyst layer 14, or the second
catalyst layer 16 can
comprise a distinct catalyst composition.
[0063] As shown in FIG. 2, the substrate member includes void spaces
provided by the
gas-flow passages 10, and the cross-sectional area of these passages 10 and
the thickness of the
walls 12 defining the passages will vary from one type of substrate member to
another.
Similarly, the weight of washcoat applied to such substrates will vary from
case to case.
Consequently, in describing the quantity of washcoat or catalytic metal
component or other
component of the composition, it is convenient to use units of weight of
component per unit
volume of substrate. Therefore, the units of grams per cubic inch ("g/in") and
grams per cubic
foot ("gift") are used herein to mean the weight of a component per volume of
the substrate
member, including the volume of void spaces of the substrate member.
[0064] In a second aspect of the invention, the catalyst of one or more
embodiments can be
used in an integrated emission treatment system comprising one or more
additional
components for the treatment of exhaust gas emissions. For example, the
emission treatment
system may comprise a lean bum engine upstream from the catalyst of one or
more
embodiments, and may further comprise a second catalyst and, optionally, a
particulate filter.
In one or more embodiments, the second catalyst is selected from a three-way
catalyst (TWC),
gasoline particulate filter (GPF), selective catalytic reduction (SCR), lean
NO trap (LNT),
ammonia oxidation (AM0x), SCR on a filter (SCRoF), and combinations thereof,
and
combinations thereof. In one or more embodiments, the particulate filter can
be selected from
a gasoline particulate filter, a soot filter, or a SCRoF. The particulate
filter may be catalyzed
for specific functions. The catalyst can be located upstream or downstream of
the particulate
filter.
[0065] In one or more embodiments, the emission treatment system may
comprise a lean
bum engine upstream from the catalyst of one or more embodiments, and may
further
comprise a TWC. In one or more embodiments, the emission treatment system can
further
comprise an SCR/LNT.
[0066] In a specific embodiment, the particulate filter is a catalyzed
soot filter (CSF). The
CSF can comprise a substrate coated with a washcoat layer containing one or
more catalysts
for burning off trapped soot and or oxidizing exhaust gas stream emissions. In
general, the
soot burning catalyst can be any known catalyst for combustion of soot. For
example, the CSF
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can be coated with a one or more high surface area refractory oxides (e.g.,
alumina, silica,
silica alumina, zirconia, and zirconia alumina) and/or an oxidation catalyst
(e.g., a ceria-
zirconia) for the combustion of unburned hydrocarbons and to some degree
particulate matter.
In one or more embodiments, the soot burning catalyst is an oxidation catalyst
comprising one
or more precious metal (PM) catalysts (platinum, palladium, and/or rhodium).
100671 In general, any known filter substrate in the art can be used,
including, e.g., a
honeycomb wall flow filter, wound or packed fiber filter, open-cell foam,
sintered metal filter,
etc., with wall flow filters being specifically exemplified. Wall flow
substrates useful for
supporting the CSF compositions have a plurality of fine, substantially
parallel gas flow
passages extending along the longitudinal axis of the substrate. Typically,
each passage is
blocked at one end of the substrate body, with alternate passages blocked at
opposite end-faces.
Such monolithic substrates may contain up to about 900 or more flow passages
(or "cells") per
square inch of cross section, although far fewer may be used. For example, the
substrate may
have from about 7 to 600, more usually from about 100 to 400, cells per square
inch ("cpsi").
The porous wall flow filter used in embodiments of the invention is optionally
catalyzed in that
the wall of said element has thereon or contained therein one or more
catalytic materials, such
CSF catalyst compositions are described hereinabove. Catalytic materials may
be present on
the inlet side of the element wall alone, the outlet side alone, both the
inlet and outlet sides, or
the wall itself may consist all, or in part, of the catalytic material. In
another embodiment, this
invention may include the use of one or more washcoat layers of catalytic
materials and
combinations of one or more washcoat layers of catalytic materials on the
inlet and/or outlet
walls of the element.
100681 The invention is now described with reference to the following
examples. Before
describing several exemplary embodiments of the invention, it is to be
understood that the
invention is not limited to the details of construction or process steps set
forth in the following
description. The invention is capable of other embodiments and of being
practiced or being
carried out in various ways.
EXAMPLES
.. EXAMPLE 1¨ PREPARATION OF CATALYST
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[0069] Ce02-A1203 particles (1A through 5A) were impregnated with a
barium acetate
solution to provide samples 1B through 5B having BaCO3/(Ce02-A1203) with a
BaCO3 content
as specified in Table 1. The mixture was dried at 110 C and calcined at 720
C for 2 hours.
[0070] Ce02-A1203 particles (4A) were impregnated with a barium acetate
solution to
provide 4C through 4E having BaCO3/(Ce02-A1203) with a BaCO3 content as
specified in
Table 1. The mixture was dried at 110 C and calcined at 620 C for 2 hours.
[0071] Ce02 particles (6A) were impregnated with a barium acetate
solution to provide 6B
and 6C having BaCO3/Ce02 with a BaCO3 content as specified in Table 1. The
mixture was
dried at 110 C and calcined at 600 C for 2 hours.
[0072] Referring to FIG. 3, after aging at 950 C for 5 hours in 2% 02 and
10% steam in
N2, the Ce02 crystallite sizes of the BaCO3/(Ce02-A1203) samples 1B-5B were
within 79 to
158 A.
100731 Referring to FIG. 4, the Ce02 crystallite sizes of the BaCO3/(Ce02-
A1203) samples
4C through 4E were within 73 to 92 A after aging at 850 C for 8 hours in 10%
steam in air.
[0074] Table 1 shows the content of IA through 6A, and 1B through 6B, 6C,
4C through
4E.
100751 Table 1
Sample BaCO3 Ce02 A1203 BET Surface Area, m2/g
wt% wt% wt% As is 950 C aged*
lA 0 30 70
2A 0 50 50
3A 0 60 40
4A 0 70 30
5A 0 80 20
6A 0 100 0 167 27
IB 26 22 52 122 79
2B 26 37 37 119 66
3B 26 44 30 93 39
4B 26 52 22 78 33
5B 26 59 15 76 21
6B 26 74 0 83 3
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4C 19 57 24
4D 13 61 26
4E 6 66 28
6C 19 81 0
*Aging conditions: 950 C for 5 hours in 2% 02 and 10% steam in N2
EXAMPLE 2¨ XRD MEASUREMENT
[0076] The Ce02 crystallite size of the Example 1 samples was measured
by XRD. The
5 samples were ground using a mortar and pestle. The resultant powders were
then back packed
into flat plate mounts for analysis. A 0-0 PANalytical X'Pert Pro MPD X-ray
diffraction
system was used to collect data in Bragg-Brentano geometry. The optical path
consisted of the
X-ray tube, 0.04 rad soller slit, 1/4 divergence slit, 15mm beam mask, 1/2
anti-scatter slit, the
sample, 1/4 anti-scatter slit, 0.04 rad soller slit, Ni filter, and a P1Xcel
linear position
10 sensitive detector with a 2.114 active length. Cuka radiation was used
in the analysis with
generator settings of 45kV and 40mA. X-ray diffraction data was collected from
100 to 90 20
using a step size of 0.026 and a count time of 600s per step. Phase
identification was done
using Jade software. All numerical values were determined using Rietveld
methods.
[0077] Reference throughout this specification to "one embodiment,"
"certain
15 embodiments," "one or more embodiments" or "an embodiment" means that a
particular
feature, structure, material, or characteristic described in connection with
the embodiment is
included in at least one embodiment of the invention. Thus, the appearances of
the phrases
such as "in one or more embodiments," "in certain embodiments," "in one
embodiment" or "in
an embodiment" in various places throughout this specification are not
necessarily referring to
the same embodiment of the invention. Furthermore, the particular features,
structures,
materials, or characteristics may be combined in any suitable manner in one or
more
embodiments. The order of description of the above method should not be
considered limiting,
and methods may use the described operations out of order or with omissions or
additions.
[0078] It is to be understood that the above description is intended to
be illustrative, and
not restrictive. Many other embodiments will be apparent to those of ordinary
skill in the art
upon reviewing the above description. The scope of the invention should,
therefore, be
determined with reference to the appended claims, along with the full scope of
equivalents to
which such claims are entitled.
