Note: Descriptions are shown in the official language in which they were submitted.
32314CAC
13~936~
OXIDATION OF CARBON MONOXIDE AND CATALYST ~HERE~OR
Background of the Invention
This invention relates to the oxidation of carbon monoxide to
carbon dioxide. In another aspect, this invention relates to the
catalytic ogidation of carbon monoxide, in particular under conditions
suitable for laser applications. In a further aspect, this invention
relates to effective CO oxidation catalyst compositions. In still
another aspect, this invention relates to a process for preparing CO
oxidation catalyst compositions.
The use of catalysts for the o~idation of carbon monoxide to
carbon dioxide by reaction with oxygen, in particular at low temperature,
is of much interest, e.g., in breathing masks designed to remove CO from
inhaled air, and in CO2 lasers for combining CO and 2 formed by
dissociation of CO2 during discharge. In the latter application, the
presence of 2 is most undesirable because it can cause a breakdown of
the electrical field in the laser cavity. Several patents, such as U.S.
Patents 4,490,4~2 and 4,~39,432, discIose compositions useful as CO
oxidation catalysts in CO2 laser applications. However, there is an ever
present need to develop new, effective CO oxidation catalyst compositions
andlor improved processes for preparing effective CO oxidation catalyst
compositions.
Summary of the Invention
It is an object of this invention to provide a composition of
matter which is effective as a catalyst for the oxidation of carbon
monoxide with free oxygen. It is another object to provide a process ior
~3~g~ 323l4rhc
preparing a co~position of matter which is effective as a catal~Jst for
the oxidation of carbon monoxide. It is a further object of this
invention to provide an effective process for catalytically oxidizing
carbon monoxide. Other objects and advantages will ~e apyarent from the
de-tailed description and the claims.
In accordance with this invention, a process for preparing a
composition of matter comprising Pt and/or Pd and TiO2 ~suitable and
efective as a catalyst composition for the oxidation of carbon monoxide
by reaction with free o~ygen) comprises the steps of:
(a) contacting (preferably impregnating)
a support material (~rom which silica is substantially absent)
comprising (preferably consisting essentially of) titanium dioxide
(titania)
with a solution comprising at least one dissolved compound of
at least one noble metal selected from the group consisting of platinum
and palladium (preferably Pt);
~ b) heating the material obtained in step (a~ under such
condltions as to substantially dry said material obtained in step ~a) and
to a-t least partially (preferably substantially) convert said at least
one compound of Pt and/or Pd to at least one of oxides of Pt, oxides of
Pd, Pt metal and Pd metal; and
(c) heating the material obtained in step (b) in a reducing
gas atmosphere, preferably a free hydrogen containing gas, more
preferably a stream of H2, at a temperature in the range of from about
300 to about 800C, under such conditions as to activate said material
obtained in step (b), i.e, to make the material obtained in step (b) more
active as a catalyst for CO oxidation by reaction with 2-
In a preferred embodiment, heating step (b) is carried out in
two sub-steps:
~bl) heating the material obtained in step (a) at a first
temperature so as to remove substantially all liquids [i.e., the solvent
of the soll-tion used in step (a)] from said material obtained in step
(a), and
(b~) heating ~calcining) the substantially dried material
obtained in step (bl) at a second temperature, which is higher than said
13 ~ 32314CA~
first temperature, so as to at leas-t partially (preferably substantially~
convert said at least one compound o~ Pt and/or Pd to at least one ~f
oxides of Pt, oxides of Pd, metallic Pt and metallic Pd (i.e., Pt oxide
and/or Pd oxide and/or Pt metal and/or Pd metal).
In another preferred embodiment, the solution used in step (a)
additionally comprises at least one dissolved compound of at least one
metal selected from the group consisting of rhenium, iron, ruthenium,
copper and silver, which are at least partially (preferably
substantially) converted to metal oxides in step (b) or, alternatively,
step (b2). In another preferred embodiment, compounds of chromium,
manganese and zinc are substantially absent (besides silica) from the
material obtained in step (c). In a further pre~erred em~odiment, the
titania support ma~erial, before its being used in step (a) has been
extracted with an aqueous acidic solution (so as to remove undesirable
impurities thereform), treated with an alkaline solution, washed (e.g.,
with water), dried, and then calcined (e.g., at about 200-800C,
preferably for about 0.5-10 hours).
In a particular 2referred embodiment, a process ior preparing a
composi-tion of matter comprising Pt and/or Pd and TiO2 (effective as a CO
oxidation catalyst composition) comprises the step of:
(A) impregnating a mono]ith material, (i.e., a porous ceramic
honeycomb material) with a colloidal dispersion (also referred to as a
colloidal solution) of titania in a suitable liquid dispersion medium
(preferably water), wherein dispersed silica is substantially absent in
said colloidal dispersion;
(B) heating the titania-coated material obtained in step (A)
so as to obtain a substantially dried titania-coated monolith material;
(C) contacting (preferably i~pregnating3 the titania-coated
monolith material obtained in step (B) ~ith a solution (preferably
aqueous), comprising at least one dissolved compound of at least one
noble metal selected from the group consisting o~ platinum and palladium
(preferably Pt);
(~) heating the material obtained in step (C~ under such
conditions as to substantially dry the material obtained in step (C) and
to at least partially (preferably substantially) convert said at least
~ 3 ~ 9 ~ 314~h5
one compound of Pd and/or Pt to at least one of oxides bf Pt, oxide~ of
Pd, Pt metal and Pd metal; and
(E) heating the material obtained in step (D) in a reducin~ gas
atmosphere, preferably a free hydrogen containing gas, mo-~e preferably a
stream of H2, at a -temperature in the range of from about 0C to about
300~, under such conditions as to activate said material obtained in
step (D), i.e., to make it more active as a C0 oxidation catalyst.
The impregnation step (A) can be carried out once or twice or
more than twice in sequence, so as to ensure adequate coating of the
monolith with TiO2. Step (D) can be carried out as a sequence of
sub-steps: drying sub-step (D1) and calcining sub-step (~2~. The
conditions of drying steps (B) and (~1) are substantially the same as
those of drying sub-step (bl), described above. The conditions of
calcining sub-step tD2~ is substantially the same as those of calcining
sub-step ~b2), described above.
Al~o in accordance with this invention, there is provided a
composition of matter (useul and effective as a catalyst composition for
the oxidation of C0 with 2), from which silica is substantially absent,
comprising (i) a support material comprising (preferably consisting
essentially of) titania and (ii) at least one noble metal selected from
the group consisting of Pt and Pd; said composition of matter having been
prepared by the process, described above, comprising steps (a), (b) and
(c); or, alternatively, steps (a), (bl), (b2) and (c); or, preferably,
steps (~), (B), (C), (D~ and (E), as definea above. Preferably said
composition of matter further comprises (iii) at least one substance
selected from the group consisting of rhenium oxide, iron oxide,
ruthenium metal, ruthenium oxide, copper metal, copper oxide, silver
metal and silver oxide, preferably iron oxide. In a more preferred
embodiment, the composition of matter o~ this invention consists
essentialIy of components (i), (ii) and (iii).
~ urther in accordance with this invention, a process for
oxidizing carbon monoxide comprises contacting a gas comprising C0 and 2
with a catalyst composition (from which silica is substantially absent~
comprising titania and at least one of Pt and Pd; said catalyst
composition having been prepared by a process comprising steps (a), (b)
13193~0 323l4chc
and ~c); or, alternatively, (a), (bl), (b2) and (c); or, preferably,
(A), (B), (C), (D) and (E), as defined above, under such conditions as to
at least partially (preferably substantially) convert CO and 2 to CO~.
Preferably, in the CO oxidation in process of this invention
the catalyst composition of this inven~ion (described above) additionall~
comprises component (iii), as defined above, preferably iron oxide (e g.,
FeO and/or Fe203 andtor Fe304). Also preferably, compounds of Cr, Mn and
~n are substantially absent from the catalyst composition (be~ides SiO2).
In a preferred embodiment, the CO oxidation process of this invention i5
carried out at a temperature of below lOO~C (more preferably from about
0C to about 90C). In another preferred embodiment, the CO oxidation
process is carried out in a CO2 laser so as to recombine CO and 2, which
have been formed by decomposition of COz.
Brief Description of the Drawings
FIGUæE 1 shows the dependence of CO conversion during low
temperature oxidation of CO upon the temperature during the reducing
pretreatment of a Pt/TiO2 catalyst with H2.
FIGURE 2 illustrates the effect of copromoters on the catalytic
activity of a PtfTiO2 catalyst when used for low temperature oxidation of
CO.
FIGURE 3 illustrates the effect of copromoters on the catalytic
activity of a Pt/Fe/TiO2 catalyst when used for low temperature oxidation
of CO.
Deta-led Description of the Invention
Any titania-containing support material can be used as the
support material (i). Titania, as the preferred support material, is
commercially available. The method of preparation of titania is not
considered critical. Titania can be prepared by flame hydrolysis of
volatile titania compounds; or by precipitation from an aqueous solution
of titanium compounds with an alkaline reagent, followed by washing,
drying and calcining; and the like. If mixtures of titania with alumina
and/or magnesia are used, any suitable weight ratio can be used ~such as
from 1-99 weight-% TiO2 and from 99-1 weight-h Al203 and/~r MgO).
&enerally the surface area ~determined by the BET/~2 method;
ASTM D3037) of titania is in the range of from about 10 to about 300
~93~ 32314C~C
m2/g. Titania can have spherical, trilobal, quadrilobal or irregular
shapes. When titania spheres are used, their diameter generally is in
the range of from about 0.5 to about 5 mm. Silica should be
substantially absent from the support material (i e., ~ilica should not
be present at a level higher than about a.5, preferably about 0.2,
weight-% each).
It is within the scope of this invention to prepare suitable
support materials by coating a honeycomb ce. ami-~ material, such as a
monolith (commercially available from Corning Glass Works, Corning, NY),
described in U.S. Patents 4,388,277 and 4,524,051, with titania. The
monolith can be impregnated with organic compounds o' Ti (such as a
titanium tetraalkoxide), hydrolyzed, dried and calcined. Or the monolith
can be impregnated with a dispersion of titania particles, followed by
drying and calcining.
In the presently more preferred embodiment of this invention, a
mon~lith is impregnated with a colloidal dispersion (colloidal solution)
of titania in step (A). Preferably, colloidal particles of titania
having an aYerage particle diameter of about 1 to about 100 nanometers,
more preferably about 5 to about 20 nanometers, are dispersed in any
suitable liquid dispersion medium, such as water, alcohols, ketones and
the like, preferably water. Generally, the concentration of TiO2 in the
colloidal dispersion is in the range of from about 0.1 to about 50,
preferably from about 5 to about 25, weight percent TiO2. The weight
ratio of colloidal dispersion of TiO2 to monolith material in step (A) is
chosen so as to provide a TiO2 content of the material obtained in step
(B) in the range of from about 1 to about 4Q weight-% TiO2, preferably
about 5 to about 30 weight-l~ TiO2.
The impregnation of the titania-containing support ma-terial
with Pt and/or Pd (preferably Pt) in steps (a) and ~c), respectively, can
be carried out in any suitable manner. ~irst, compounds of Pt and/or Pd
are dissolved in a suitable solvent (preferably water) so as to prepare
solutions of suitable concentration, generally containing from about
0.005 to about 0.20, preferably about 0.01 to about 0.1, g Pt and/or Pd
per cc of solution. Non-limiting examples of suitable compounds of Pt
and Pd are: PtCl2, PtCl4, H2PtCl6, PtBr4, Pt(NH3)4cl2~ PtlNH3)~(~03)2
~ ~193~ 323l4rA~
and the like; PdC12, PdCl4, H2PdCl6, Pd(NH3)4(NO3)2 and the like;
preferably (at present) Pt(NH3)4(NO3)2 and Pd(NH3)4(N03)2. The
TiO2-containing support material is then impregnated by soaking it in the
solution of Pt and/or Pd compounds; or (less preferably) the Pt and/or
Pd containing solution is sprayed onto the support material. The ratio
of Pt and/or Pd containing solution to support material generally is such
that the final catalyst obtained in step (c) or, alternatively, the
coating of the material obtained in (~), i.e., the material obtained in
step (E) excludi~g the monolith, contains about 0.5 to about 5,
preferably about 1 to about 3, weight-~ Pt or Pd. When a solution
containing both Pt and Pd compounds, the level of Pt and Pd generally is
about 0.5 to about 5, preferably about 1 to about 3, weight percent
(Pt+Pd).
In a preferred embodiment, at least one compound of a metal
selected from the group of Re, Fe, Ru, Cu and Ag, more preferably Fe, is
also present as a copromoter in the impregnating solution (besides Pt
and/or Pd). Non-limiting examples of suitable Fe compounds that can be
used as solutes are FeCl2, FeCl3, Fe2(S04)3, Fe(N03)2, Fe(N03)3 and the
like, preferably compounds of Fe in the valence state ~3, more preferably
Fe(~03)3. Non-limiting examples of Nn compounds are MnCl2, MnS04,
MntNO3)2, KMnO4, and the like. Non-limiting examples of Ru compounds are
RuCl3, RuE4, Ru~NH3)6Cl3, KRu04, and the like. Non-limiting examples of
Cu compounds are CuC12, Cu~NO3)2, GuS04, Cu(II) acetate, ammine complexes
of the above Cu salts, and the like. Non-limiting examples of Ag
compounds are AgF, AgN03, Ag2S04, Ag acetate, ammine complexes of the
above Ag salts, and the like.
Cenerally, the concentration of the copromoter compound
(expressed as metal) is in the ran8e of from about 0.01 to about 0.4,
preferably about 0.02 to about 0.2, g metal (i.e., Mn or Fe or Ru or Cu
or Ag or mixtures thereof) pex cc solution. When a mixture of copromoter
compounds is used, e.g., a mixture of compounds of Fe and Ru, Fe and Ag,
Ru and Cu, Fe/Ru/Ag, and the like, the total concentration of copromoter
metals is about 0.02-0.8 g/cc. The impregnation of the support material
with Pt and/or Pd and the copromoter method can be carried out either by
sequential impregnation (first Pt and/or Pd, then copromoter) or by
13 ~ 9 3 ~ ~ 32314CAC
simultaneous impregnation in step (a) or, alternatively, step (C~ (using
a solution containing Pt and/or Pd compounds and at least one copromoter
compound).
When sequential impregnation is employed, the impregnation with
a solution of at least one copromoter compound is carriPd out after
heating step (b) and before step (c); or, if applicable, after heating
step (D) and before step (E). Thus, an impregnating step (a*) with at
least one dissolved copromoter compound and heating step (b*) [carried
out in substantially the same manner as step (b)] are performed after
step (b) and before step (c). Similarly, an impregnation atep (~') ~ith
at least one dissolved copromoter compound and heating step (D*) [carried
out in substantially the same manner as step (D)] are performed after
step (D) and before step (E). The ratio of copromoter containing
solution to support material is such as to provide a level of about 0.2
to about 4, preferably about 0.5-2, weight percent copromoter metal
~i.e., Re or Fe or Ru or Cu or Ag, or mixtures of two or more metals,
(e.g., Fe/Ag, and the like) on the material obtained in step (c) or,
alternatively, on the material obtained in step (~) excluding the
monolith.
Preferably compounds of Cr, Mn and Zn should be substantially
absent from the impregnating solutions used in impregnation steps (a),
(a~), (C) and (C~) since these compounds have a detrimental effect on the
activity for C0 oxidation of the finished catalyst.
Heating step (b) is generally carried out in an inert or
oxidizing atmosphere, preferably a free oxygen containing gas atmosphere
(such as air), generally at a temperature ranging from about 30 to about
700C. Preferably, heating step tb) is carried out in tWQ sequential
sub-steps: sub-step (bl), at about 3a to about 200C (preferably at
30-130C~, generally for about 0.5 to about 10 hours, so as to
substantially dry the impregnated material obtained in step (a)
(preferably under such conditions as to reduce the level of adhered and
accluded water to less than about 20 weight-~O)j and sub-step (b2), at
about 300 to about 700C (preferably about 400 to about 600C), generally
for about 1 to about 20 hours, under such conditions as to substantially
calcine the impregnated support material so as to obtain oxides of Pt
131936~ 32314CAC
and/or Pd, on titania. When compounds of Re, Fe, Ru, Cu or Ag or
mixtures thereof have been present in the Pt and/or Pd-containing
impregnating solution, gene-rally oxides of Re, Fe, Ru, Cu and/or Ag are
formed in step (b2).
Drying sub-steps (b~l), (Dl~ and (D*l), described above, are
carried out at conditions which are essentially the same a~ ths~e
described for sub-step (bl). And calcining sub-steps (b*Z) 7 (D2) and
(D-~2), described above, are carried out at conditions which are
essentially the same as those described for sub-step (b2)
Reducing step (c) can be carried out in any suitable manner at
a temperature in the range of from about 300 to about 800C, preferably
rom about 350 to about 500~C. Reducing step (~) can be carried out in
any suitable manner at a temperature in the range of from about 0 to
about 300C, preferably about 20 to about 200C. Any reducing gas can be
employed in reducing steps (C) and (E~, such as a gas comprising H2, C0,
gaseous hydrocarbons such as methane, mixtures of the above, and the
like. Preferably, a free hydro~en containing gas, more preferably
sub~tantially pure H2, is employed. Reducing steps (c) and (E) can be
carried out for any suitable period of ~ime suitable to activate the
calcined material obtained in the previous step, preferably from about
0.5 to about 20 hours.
The process for oxidizing a carbon monoxide containing feed gas
can be carried at any suitable temperature and pressure conditions, for
any suitable length of time, at any suitable gas hourly space velocity,
and any suitable volume ratio of C0 and 2 The reaction temperature
generally is in the rang eof from about 0 to about 400C, preferably
about 0 to about 100C, more preferably from about 10 to about 50C, most
preferably about 20-4aoc. The pressure during the oxidation process
generally is in the range of from about 1 to about 2,000 psia, more
preferably from about 5 to about 20 psia. The volume ratio of C0 to 2
in the feed gas can range from about 1:100 to about 100:1, and preferably
is in the range of about 1:10 to about 10:1. The volume percentage of C0
and the volume percentage of f 2 in the feed gas can each be in the
range of from about 0.05 to about 50, preferably from about 0.5 to about
3. The gas hourly space velocity (cc feed gas per cc catalyst per hour)
13~936~ 32314ChC
can be in the range of from about 0.5 to about 10,000, preferably from
about 1 to about 1,000. It is understood that the calculation of the ~a~
hourly space velocity is based on the volume of the active catalyst i.e ,
the titania-supported Pt and/or Pd catalyst toptionally also contaiuing
copromoter), excluding the volume occupied by any additional ~upport
material, such as a monolith material.
The feed gas can be formed in any suitable manner, e g., by
mixing C0, 2 and optionally other gases such as CO2, N2~ He and the
like, such as in a carbon dioxide laser cavity. Or the feed gas can be
an exhaust gas from a combustion engine, or it can be air that is to be
inhaled by humans and contains undesirable levels of toxic carbon
monoxide, and the like. The feed gas can be contacted in any suitable
vessel or apparatus, such as in a laser cavity or in an exhaust pipe of a
combustion engine, or in a gas mask used by humans, wherein the feed gas
passes over the catalyst composition of this invention at the conditions
described above. The CO oxidation process of this invention can be
carried out in any suitable setting and for any purpose, e.g., for
recombining C0 and 2 in CO2 lasers, to oxidize CO contained in exhaust
gases or air, to make isotopically labeled CO2 from CO and the 1~o
isotope, and the like.
The following examples are presented in further illustration of
the invention and are not to be construed as unduly limiting the scope of
the invention.
Example I
This example illustrates the experimental setup for testing the
activity of noble metal catalysts for catalyzing the oxidation of carbon
monoxide (so as to simulate catalytic recombination of C0 and 2 in CO2
lasers). A gaseous feed blend comprising C0, 2, ~le and ~2 was passed
through a needle valve and a glass reactor in an upflow direction. The
glass reactor tube had an inner diameter of about 6 mm and generally
contained about 1.0 gram catalyst in a bed of about 2.5 cm height. The
temperature in the catalyst bed was measured by means of a thermocouple
inserted into the top layer of the catalyst bed. The CO content in the
reactor effluent was determined by means of a Beckman Model 864 IR
analyzer.
131936~ 32314CAC
11
All tests were carried out at ambient conditions. Generally
the temperature in the catalyst bed rose to about 30C because of the
generation of hPat during the 50 oxidation tests. The feed rate of the
gaseous feed stream generally was in the range of about 4-300 cc/minute.
Example II
This example illustrates the preparation of titania-supported
catalyst compositions and their performance in CO oxidation testg.
Catalyst A1 con-tained 1 weight-% Pt on TiO2 ~t was prepared
by mixing, a~ room temperature, 30 g of flame-hydrolyzed titania
(provided by Degussa Corporation, Teterboro, NJ; having a B~T/N2 surface
area of about 50 m2/g) with 31 cc of aqueous chloroplatinic acid
solution, which contained 0 0096 g Pt/cc solution, and enough distilled
water to form a thick paste After impregnation, Catalys~ Al was dried
at about 125C for several hours and calcined in air at about 350C for
about 6 hours Catalyst Al was then pretreated with hydrogen gas for
about 4 hours at various temperatures (range: 200-725C)
Samples of catalyst A1 (1% Pt/TiO2) that had been pretreated
with H2 at different temperatures was tested at room temperature (about
27GC) in the C0 oxidation unit described in E~ample I. The gaseous feed
blend contained 1.2 volume-~/O C0, 0.6 volu~e-/O 2~ 40.7 volume-% N2 and
57.5 volume-% He. The feed rate was 10 cc/minute. The ~orrelation
between C0 conversion and the temperature of the hydrogen pretreatment
temperature of Catalyst Al is shown in Figure 1. Figure 1 shows that H2
pretreatment of the Pt/TiO2 catalyst at temperatures in the range of 400
to 725C resulted in a considerably more active C0 oxidation catalyst
than H2 pretre~tment at 200C.
Catalyst A2 contained 1 weight-l~ Pt and 0 3 weight-b Pd on
TiO2, and was prepared by mixing 30 g Catalyst Al with 100 cc of an
aqueous solution containing 0.25 g tetramminepalladinum(II) nitrate,
drying and calcining the obtained paste as described for Catalyst Al.
The calcined Catalyst A~ material was then activated by heating with H2
at 725C for 16 hours C0 conversion tmeasured as described for the
tests employing Catalyst A1) was 100% for about 126 hours. Thus, Pd
enhanced the C0 o~idation activity of the Pt/TiO2 catalyst.
3 1 9 ~ 6 ~ 32314CAC
~xample III
This example illustrates the effects of various other
copromoters on the C0 oxidation activity of a Pt/TiO2 catalyst which
contain~d 2 weight-% Pt (labeled Catalyst Bl) and was prepared
substantially in accordance with the procedure for Catalyst Al, e-~cept
that the Pt concentration in the impregnating solution was thrice as
high, and the TiO2 support material was provided by Calsicat (division of
Mallinckrodt, Inc., St. Louis, MO) and had a BET surface area sf about
40-170 m2/g.
Catalyst Bl was then mixed with aqueous solutions containing
different metal compounds so as to provide a copromoter level of 0.8
weight-% of the metal. A solution of tetramminepalladinum(II) nitrate
was used to make Catalyst B2 (0.8% Pd/2% Pt/TiO2~. A solution of
Ru~13 3H20 was used to make Catalyst B3 (0.8% Ru/2% Pt/Ti2) A
solution of ReCl3 was used to make Catalyst B4 (0.8% Re/2% Pt/TiO2). A
sGlution of hexamminechloroiridium(II) dichloride was used to make
Catalyst B5 (0.8% Ir/2% Et/TiO2~. A solu~ion of Cu(N03)2 2.5H20 was used
to make Catalyst B6 (0.8b Cu/2% Pt/TiQ2). A solution of Fe(N03) 9H20 was
used to make Catalyst B7 (0.8% Fe/2/O Pt/TiO2).
C0 conversions attained at room temperature (about 27C) in the
test unit of Example I employing a gas ieed containing 1.2 volume-% CO,
0.6 volume-/O 2, 48 volume-/O N2 and He as the balance (flow rate of feed:
10 cc/minute), are shown for Catalysts B1, B2, B3, B4, B5, B6 and B7 in
Figure 2. All catalysts had been pretreated with hydrogen gas for 3
hours at 600C.
The graphs in Figure 2 indicate that Fe, Pd, Re, Ru and Cu
consistently enhanced the C0 oxidation activity of the Pt/TiO2 base
catalyst, whereas Ir enhanced the C0 oxidation ac-tivity of the base
catalyst only up to 60 hours on stream. Additional test data (not shown
in Figure 2~ indicated that Rh did not affec~ the catalytic activity of
the PtlTiO2 base catalyst. Fe, Pd and Re were the most effective
copromoters for the Pt/TiO2-containing C0 oxidation catalyst.
In another test series, a TiO2-supported catalyst containing
0.4 weight-h Fe and 2.0 weight-b Pt, labeled Catalys-t B8, was prepared
substantially in accordance with the procedure for Catalyst B7 t except
~ 3 ~ 32~14CAC
13
for a lower Fe level. Catalyst B8 was then impregnated tlith an aqueo~s
solution containing a compound of a third promoter metal, so as to obtain
Catalysts _ , Bl0, Bll and B12, respectively, containing 0.1 weight % o~
the following third promoter elements: Mn, Cr, Ag and Zn. Carbon
5 monoxide conversions, attained by Catalysts B8, B9, B10 and Bll at room
temperature (about 27C) in the test unit of Example I employing the gas
feed described in Example II are shown in Figure ~. The gas feed rate
was 60 cc/minute (in lieu of 10 cc/minute). All catalysts had been
pretreated in hydrogen gas for 3 hours at about 500C. The TiO2 support
had been heated in H2 for about 48 hours at 500C before impregnation
with the promoters (Fe, Pt ~ third promoter) for removal of traces of
sulfur in TiO2.
The graphs in Figure 3 indicate that Ag enhanced the activity
of the Fe~Pt/TiO2 C0 oxidation catalyst, whereas the presence of Mn, Cr
and Mn was detrimental. Based on these test results, it is concluded
that Ag i5 also an effective promoter for a Pt/TiO2-containing catalyst
(with or without Fe).
Example IV
This example illustrates a preferred feature of the preparation
of TiO2-supported Pt catalysts useful for C0 oxidation at low
temperature. Two catalysts containing 0.5 weight-% Fe, and 2.0 weight-%
Pt on Calsicat TiO2 support were tested. Catalyst Cl was prepared
substantially in accordance with the preparation of Catalysts B7 and B8,
using an aqueous solu-tion of chloroplatinic acid. Catalyst C2 was
prepared as described above except that the dissolved Pt compound was
te~rammineplatinum(II) nitrate. The two catalysts were dried, calcined
and pretreated with hydrogen gas at 500C for about 3 hours, as has been
described in ~xamples II and III.
The two catalysts were tested at room temperature (about 26C)
in the C0 oxidation test unit described in E~ample I, employing the gas
feed described in Example III. The gas ~eed rate was 120 cc/minute.
Test results are summarized in Table I.
13~936B 3Z~14CAC
14
Table I
Hours on % C0 cclMinute
Catalyst Stream Converted C0 Con~erted
Cl 2 60 ~.84
6 56 0 7~
1~ 56 0.78
1~ 55 0.77
~0 55 0.77
301 50 0.70
~0 401 44 0.62
C2 2 63 0,89
6 70 0.98
78 1.09
89 1.25
94 1.3Z
92 1.30
92 1.3
1.2
91 1.27
~0 lTemperature had dropped to 23C.
Test results in Table I clearly show that the Fe/Pt/TiO2
catalyst prepared using a chloride-free Pt compound for impregnation
(Catalyst C2) was consistently more active for C0 oxidation than Catalyst
Cl, which had been prepared using a chloride-containing Pt compound for
impregnation.
Example V
This example illustrates how the C0 oxidation activity of a
TiO2-supported catalyst can be enhanced by pretreatment of the TiO2
support.
25 grams of flame-hydrolyzed titania (provided by Degussa
Corporation; see Example II) was stirred overnight in a mixture of ~00
cc concentrated H2SO~ and 300 cc deionized water. The aqueous slurry of
titania was then neutralized wi~h a concentrated ammonia solution. The
-dispersed titania was allowed to settle, and the supernatant solution was
decanted. The thus treated titania was washed four times with deioni~ed
water and dried in a circulating air oven (80-90C; 5 hours3.
S grams of the acid-treated TiO2 was impregnated with 3 cc of
an aqueous solution of Pt(NH3)4(NO~)2 (containing 0.033 g Pt per cc) and
13193~ 32314CAC
then with 2.5 cc of an aqueous solution of Fe(~03)3 ~containing ~ 01 g ~e
per cc~. The thus impregnated material was dried, calci~ed and
pretreated with hydrogen gas for 3 hours at 500C. This catalyst,
labeled Catalyst D, contained 2 weight-~ Pt and 0.5 weight-% Fe
Catalyst D was compared to Catalyst C2 (see ~xa~ple IY; also
containing 2 weight-% ~e on TiO2) which had been prepared without acid
treatment of titania (provided by Degussa Corporation). The two
catalysts were tested at room temperature (27-29gC) in the C0 o~idation
test unit described in Example I, employing the gas feed described in
~xample III. Test results are summarized in Table II.
Table II
Gas Feed Hours on % C0 cc/Minute
CatalystRate (cc/min.) Stream ConvertedC0 Converted
-
D 160 2 58 1.09
15 (TiO2 Support " 4 65 1.22
Acid-Treated) " 6 68 1.28
" 10 68 1.28
" 14 68 1.28
" 18 67.5 1.26
" 22 67.5 1.26
C2 120 2 56 ~.79
(TiO2 Support " 4 48 0.67
Not Acid-Treated) " 6 43 0.60
" 10 41 0.58
25" 14 41 0.58
" 18 ~2 0.59
Data in Table II clearly indicate that the C0 conversion was
greater for Catalyst D as compared to Catalyst C2 in spite of the higher
gas feed rate of the run with Cataly~t D. The conversion of C0,
expressed in cc C0 converted per minute, attained by Catalyst D was about
twice that attained by Catalyst C2.
Thus, in the presently preferred catalyst preparation method of
this invention, the TiO2 support material is treated with an aqueous acid
solution, followed by neutralization and washing, before the TiO2 support
material is impregnated with promoters, dried, calcined and heated in H~
gas.
32314CAC
16 1~93~
~xample VI
This example illustrates the use of honeycomb ceramic catalyst
supports, called monoliths, for preparing Pt/TiO2-containing catalysts
employed in the oxidation of carbon monoxide. The two best modes of
preparation of these honeycomb catalysts are described in this example.
Mode A: A round piece of Celcor~ Cordierite #9475 monolith
ceramic material 2MgO 2Al203 5SiO2; provided by Corning Glass Works,
Corning, NYi diameter: 1 inch; height 1 inch; having 100 cells per
square inch) was dried for 2 hours at 185C, and was then dipped about 7
times into a stirred suspension of 30 grams flame-hydrolyzed TiO2
(Degussa Corporation) in 250 cc distilled water. The material was dried
a$ter each dipping. This TiO2-coated monolith material was calcined in
air for 4 hours at 500C. The calcined TiO2-coated monolith material was
then dipped into an aqueous solution of chloroplatinic acid (containing
0.022 g Pt/cc), dried for 1 hour at 300C, dipped into an a~ueous
solution of Fe~N03)3 (containing O.Ol g Fe/cc) and dried again for 1 hour
at 300C. The Fe/Pt/TiO2/monolith catalyst, labeled Catalyst El, was
pretreated in hydrogen gas for 3 hours at 500~C and then heated in helium
gas at that temperature for 30 minutes. The impregnation with Pt and Ee,
drying and pretreating with H2 was repeated.
Catalyst El was tested in a C0 oxidation apparatus at room
temperature (about 26C) in an apparatus similar to the one described in
Example I, except that a glass reactor tube of l inch inner diameter was
used. The $eed gas employed was essentially the same as the one
described in Example III. Test results are summarized in Table III.
1 ~19~ 323~4CA~
17
Table III
Hours on Gas Feed % C0 cc/Minute
Stream Rate (cc/min.)ConversionC0 Converted
4 10 99 O.lZ
99 0.12
18 10 99 0 12
96 0.34
24 30 96 ~.34
g1 0.64
0.56
72 0.50
66 0.46
5~ 0.41
0.42
58 0.41
100 60 56 0.40
~10 60 55 0.38
Mode B: The presently best mode for preparing honeycomb-type
Pt/TiO2-containing catalysts is as follows. A piece of Cordierite 9475
monolith material (diameter: 1 inch; height: 1 inch) was dipped into a
colloided solution of TiO2 in water (provided by Nalco; containing about
6 weight-~ TiO2 having an average particle diameter of ~ microns). The
monolith piece was dipped 9 times into the colIoidal TiO2 solution. The
thus impregnated piece was dried at 150C after each dipping. The
TiO2-coated monolith was then dipped into an aqueous Pt(~H3)~(N~3)2
solution (containing 0.33 g/cc Pt), dried, calcined in air for 2 hours at
300C, and pretreated in H2 gas after 1 hour at room temperature (25C).
The coating of the thus-prepared catalyst, labeled Catalyst E2, contained
about 3 weight-% Pt and about 97 weight-% TiO2.
~ y~ was prepared by dipping E2 into an aqueous solution
of Fe(N03)3 (containing 0.01 g Fe per cc), drying, calcining in air for 2
hours at 300C, and pretreating in H2 for 1 hour at room temperatnre.
The coating of Catalyst E2 contained about 3 weight-~ Pt, about 1
weight-% Fe and 96 weight-% TiO2.
Catlayst E4 was prepared by dipping E3 into an aqueous solution
of Pd~NH3)4(N03~2 (containing 0.04 g Pd per cc), calcining in air for 2
hours at 300C, and pretreating with H2 for 1 hour at room temperature.
Catalysts E2, E3 and E4 were tested in the experimental setup
described for the C0 oxidation run employing Catalyst E1. The gas feed
~3~93~ 32314CAC
18
rate for all runs was 300 cc/minute. Test results are summarized in
Table IV.
Table IV
Hours on /~ C0 cc/Minute
Catalyst S~ream Conversion C0 Converted
E2 1 9.4 0 33
2 8.5 0.30
4 4.3 0 15
E3 1 74 2 61
2 6g 2 43
4 60 2 10
6 58 2 04
54 1 89
14 51 1 80
47 1 65
E4 1 93 3 27
2 83 2 91
4 73 2 55
6 69 2.43
1.92
14 47 1.65
33 1.17
Test results in Table IV indicate that high C0 conversions (cc
C0/minute) were attained at high gas feed rates (300 cc/minute; higher
than in any previous run). Thus the monolith-supported catalysts E2-E4,
prepared by impregnation with colloidal TiO2, are considered the
presently best TiO2-supported C0 oxidation catalysts.
A run not listed in Table IV employing a catalyst similar to
Catalyst E3, except that 0.6 weight-% Mn was prepared in the coating in
lieu of 1 weight-% Fe, gave C0 conversions of only about 33% and about
1.2 cc CO/minute during the first 5 hours. Thus, Mn/Pt/TiO2 catalysts
are not considered more preferred catalysts of this invention.
A particular advantage of the monolith-supported
Pt/TiO2-containing catalysts E2-E4 is that they could be activated by
pretreatment in H2 at a low temperature (about 25C), whereas the
catalysts used in previous examples required pretreatment in H2 at an
elevated temperature (e.g., 400-500C). In fact, reheating Catalyst E4
~3193~ 32314CAC
19
for 3 hours in air at 500C and then for 1 hour in hydrogen at 400C ~ade
this catalyst substantially inactive for C0 oxidation.
Example VII
A test employing a catalyst, which contained 1 wei~ht-% Pt on
SiO2 and had been pretreated in H2 at 660C for about 1 hour, showed no
activity for catalyzing the oxidation of C0 at room temperature. Thus,
SiO2 should be substantially absent from the ca-talyst of this invention.
Reasonable variations t modifications and adaptations for
various usages and conditions can be made within the scope of the
disclosure and the appended claims, without departing from the scope of
this invention.
