U.S. patent application number 15/933446 was filed with the patent office on 2018-07-26 for catalyst for low temperature emission control and methods for using same.
The applicant listed for this patent is University of Tennessee Research Foundation, UT-Battelle, LLC. Invention is credited to Andrew J. Binder, Sheng Dai, James E. Parks, II, Todd J. Toops.
Application Number | 20180207624 15/933446 |
Document ID | / |
Family ID | 57147256 |
Filed Date | 2018-07-26 |
United States Patent
Application |
20180207624 |
Kind Code |
A1 |
Parks, II; James E. ; et
al. |
July 26, 2018 |
CATALYST FOR LOW TEMPERATURE EMISSION CONTROL AND METHODS FOR USING
SAME
Abstract
The invention provides a composite catalyst containing a first
component and a second component. The first component contains a
ternary mixed metal oxide. The second component contains a platinum
group metal. The composite catalyst is useful for catalyzing the
low temperature oxidation of carbon monoxide and hydrocarbons.
Inventors: |
Parks, II; James E.;
(Knoxville, TN) ; Dai; Sheng; (Knoxville, TN)
; Toops; Todd J.; (Knoxville, TN) ; Binder; Andrew
J.; (Knoxville, TN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UT-Battelle, LLC
University of Tennessee Research Foundation |
Oak Ridge
Knoxville |
TN
TN |
US
US |
|
|
Family ID: |
57147256 |
Appl. No.: |
15/933446 |
Filed: |
March 23, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15134449 |
Apr 21, 2016 |
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15933446 |
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62151488 |
Apr 23, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F01N 3/103 20130101;
B01J 23/42 20130101; B01J 2523/845 20130101; B01J 37/04 20130101;
B01J 2523/17 20130101; B01D 2255/20746 20130101; B01D 53/944
20130101; B01D 2255/2065 20130101; B01J 2523/3712 20130101; B01J
35/0006 20130101; Y02A 50/2341 20180101; B01D 2255/20761 20130101;
B01J 35/002 20130101; B01D 2255/102 20130101; B01J 2523/00
20130101; B01J 23/894 20130101; B01J 23/002 20130101; B01J 23/83
20130101; Y02A 50/20 20180101; B01J 37/035 20130101; B01J 37/03
20130101; B01J 2523/00 20130101; B01J 2523/17 20130101; B01J
2523/31 20130101; B01J 2523/3712 20130101; B01J 2523/828 20130101;
B01J 2523/845 20130101; B01J 2523/00 20130101; B01J 2523/17
20130101; B01J 2523/3712 20130101; B01J 2523/845 20130101 |
International
Class: |
B01J 23/89 20060101
B01J023/89; B01J 23/83 20060101 B01J023/83; B01J 23/00 20060101
B01J023/00; B01J 23/42 20060101 B01J023/42; B01D 53/94 20060101
B01D053/94; B01J 35/00 20060101 B01J035/00; B01J 37/03 20060101
B01J037/03; B01J 37/04 20060101 B01J037/04 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] The United States Government has rights in this invention
pursuant to contract no. DE-AC05-00OR22725 between the United
States Department of Energy and UT-Battelle, LLC.
Claims
1. A composite catalyst comprising: a. a first component comprising
a ternary mixed metal oxide, wherein said ternary mixed metal oxide
comprises copper oxide, cobalt oxide, and cerium oxide; and b. a
second component comprising a platinum group metal.
2. A composite catalyst according to claim 1, wherein the composite
catalyst catalyzes the oxidation of CO to CO.sub.2 at or around
150.degree. C.
3. A composite catalyst according to claim 1, wherein the platinum
group metal is selected from the group consisting of ruthenium,
rhodium, palladium, osmium, iridium, platinum, and combinations
thereof.
4.-6. (canceled)
7. A component in an exhaust system in an engine comprising the
composite catalyst of claim 1.
8. An emission control system comprising the composite catalyst of
claim 1.
9. A motor vehicle comprising the composite catalyst of claim 1.
Description
RELATED APPLICATIONS
[0001] This application asserts the priority of U.S. Provisional
Application Ser. No. 62/151,488 filed on Apr. 23, 2015, the
contents of which are incorporated herein by reference.
FIELD OF THE INVENTION
[0003] The present invention provides a catalyst for low
temperature oxidation of carbon monoxide, hydrocarbons, and nitric
oxide.
BACKGROUND OF THE INVENTION
[0004] Removing the harmful pollutants in engine exhaust has been
an intense focus of the automotive, trucking, and off-road engine
industries over the last several decades. Increasingly stringent
emissions regulations worldwide have driven the introduction of
engine improvements and catalysts and other aftertreatment for
emissions control. In particular, the emissions regulations for
fuel-efficient diesel engines that were implemented in 2007 and
2010 have resulted in a new generation of emissions control
products. Among the products are catalysts that oxidize pollutants
such as CO and hydrocarbons (HCs); these catalysts usually reach
90% conversion of pollutants between 200.degree. C. and 350.degree.
C., but below these temperatures, the catalysts are relatively
inactive.
[0005] Consequently, more than 50% of a vehicle's pollutant
emissions occur in the first 2-3 minutes of the transient drive
cycle required for certification and under "cold-start" or idling
conditions. Thus, as emissions regulations become more stringent,
meeting the emission regulations will require increased activity
during this warm-up period.
[0006] To further complicate matters, the increased Corporate
Average Fuel Economy standards that will be implemented over the
next decade will result in the introduction of more fuel-efficient
engines. Higher fuel efficiency will result in less heat lost to
exhaust and lower exhaust temperatures, which further necessitates
the need for increased emissions control activity at low
temperatures. With this in mind the U.S. DRIVE Advanced Combustion
& Emissions Control Technology Team has set a goal of achieving
90% conversion of CO/HC/NOx at 150.degree. C. Such an aggressive
goal is designed to address the challenges associated with meeting
U.S. Environmental Protection Agency Tier 3 emission regulations
for light-duty vehicles which phases in between 2017 and 2025 as
well as other new emission regulations across the world.
[0007] Although great progress has been made through decades of
research and development on the existing material combinations used
for oxidation catalysts, further increase of low temperature
performance is difficult. The platinum group metals (PGMs) Pt, Pd,
and Rh are the active component in essentially all commercial
oxidation catalysts. Increasing PGM loadings may help to increase
the catalytic efficiency, but as PGM content is increased,
maintaining a highly dispersed PGM surface becomes more difficult.
This is due to the problem that as more PGM is added, larger PGM
particles result which have less surface area to mass than the more
finely dispersed smaller PGM particles associated with lower PGM
loadings on catalysts. Since all catalytic reactions occur on the
surface, the decreased surface area per added PGM causes the
approach of increasing PGM content to be too expensive for long
term success.
[0008] Furthermore, while PGM materials are active for both CO and
HC oxidation reactions, both CO and HC readily chemisorb to the PGM
surface which can create competition between the species for access
to PGM sites where the oxidation process occurs. Such competition
that decreases catalytic activity is known as "inhibition" and has
been a major limiting factor in the low temperature activity of
catalysts for engine emission control. Essentially, HCs in the
exhaust stream can bind to the PGM surface and, at temperatures
where no reactivity of HCs occurs, fully occupy the surface thereby
preventing adsorption and reaction of CO. The same inhibition
process can occur in reverse with CO masking PGM access to HCs.
Thus, oxidation of CO and HCs is much more difficult when both
pollutants are in the exhaust stream especially at low temperatures
where oxidation reactions of either species does not occur
rapidly.
[0009] It is important to note that a new family of advanced
combustion variants for engines are being developed that attain
higher fuel efficiency via increasing the homogeneity of combustion
which lowers the internal combustion process temperatures in the
engine cylinder. Such combustion techniques are known as "low
temperature combustion" and have the benefits of higher fuel
efficiency (as compared with conventional diesel combustion) and
lower NOx and particulate matter emissions (due to the more
homogenous combustion process and lower combustion temperatures).
However, as expected, the exhaust observed from low temperature
combustion engines has been shown to have lower temperature (as
compared with conventional diesel engine exhaust) and increased CO
and HC emissions (as more fuel components escape combustion due to
the homogeneous charge and lower combustion temperatures). For
these promising combustion techniques, the combination of lower
exhaust temperatures and the potential for inhibition between CO
and HC oxidation over PGM catalysts creates an even greater
challenge.
[0010] In summary, the utility of existing PGM-based oxidation
catalysts is insufficient for the combination of new emission
requirements and changing exhaust conditions of new fuel-efficient
engine technologies.
BRIEF SUMMARY OF THE INVENTION
[0011] The above needs have been met by the present invention,
which provides, in one aspect, a composite catalyst comprising a
first component comprising a ternary mixed metal oxide; and a
second component comprising a platinum group metal. The composite
catalysts are useful for low temperature oxidation of carbon
monoxide and hydrocarbons. In one embodiment, the carbon monoxide
and hydrocarbons are fully oxidized to non-harmful carbon dioxide
and water. In another embodiment, the composite catalysts can also
oxidize nitric oxide to nitrogen dioxide which is an important
process step in the control of particulate matter and nitrogen
oxide emissions by other filter and catalyst components further
downstream in the exhaust system. The composite catalyst can be
useful in numerous systems, such as in a component in an exhaust
system in an engine, an emission control system, a motor vehicle,
etc.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1A Oxidation efficiency of CO constituents of the gas
stream as a function of inlet gas temperature for the CCC,
Pt/Al.sub.2O.sub.3, and CCC+ Pt/Al.sub.2O.sub.3 catalysts.
[0013] FIG. 1B Oxidation efficiency of C.sub.3H.sub.6 constituents
of the gas stream as a function of inlet gas temperature for the
CCC, Pt/Al.sub.2O.sub.3, and CCC+ Pt/Al.sub.2O.sub.3 catalysts.
[0014] FIG. 1C Oxidation efficiency of C.sub.3H.sub.8 constituents
of the gas stream as a function of inlet gas temperature for the
CCC, Pt/Al.sub.2O.sub.3, and CCC+ Pt/Al.sub.2O.sub.3 catalysts.
[0015] FIG. 2 CO oxidation efficiency in the presence or absence of
C.sub.3H.sub.6 for the CCC and Pd/ZrO.sub.2--SiO.sub.2
catalysts.
[0016] FIG. 3A DRIFTS spectra for CCC catalyst.
[0017] FIG. 3B DRIFTS spectra for Pd/ZrO.sub.2--SiO.sub.2
catalyst.
[0018] FIG. 4A STEM including EDX analysis of atomic composition
for Ce.
[0019] FIG. 4B STEM including EDX analysis of atomic composition
for Co.
[0020] FIG. 4C STEM including EDX analysis of atomic composition
for Cu.
[0021] FIG. 4D STEM including EDX analysis of atomic composition
for Ce-, Co-, and Cu-oxide phases.
[0022] FIG. 5A Oxidation efficiency of CO over the binary mixtures
as compared with the ternary mixed metal oxide CCC catalyst.
[0023] FIG. 5B Oxidation efficiency of C.sub.3H.sub.6 over the
binary mixtures as compared with the ternary mixed metal oxide CCC
catalyst.
[0024] FIG. 6 C.sub.3H.sub.6 oxidation efficiency as a function of
temperature for different methods of combing the ternary mixed
metal oxide and platinum group metal catalyst components.
DETAILED DESCRIPTION OF THE INVENTION
[0025] In one aspect, the invention provides a composite catalyst
capable of low temperature oxidation, such as oxidation of carbon
monoxide (CO) and oxidation of hydrocarbons. A composite catalyst
in accordance with the claimed invention contains a first and
second component.
[0026] The first component comprises a ternary mixed metal oxide. A
ternary mixed metal oxide is comprised of three different metal
oxides. A metal oxide is typically composed of a metal and at least
one oxygen atom. Any metal oxide can be used in the ternary mixed
metal oxide of the invention. The metal component of the metal
oxide can be, for example, cobalt, copper, cerium, iron, manganese,
magnesium, aluminum, silver, gold, etc. In one embodiment, the
ternary mixed metal oxide is copper oxide-cobalt oxide-cerium
oxide. Cerium oxide is commonly known as ceria. The ternary mixed
metal oxide copper oxide-cobalt oxide-cerium oxide is described in
for example, Liu et al. (Applied Catalysis A: General, 451 (2013)
282-288); and Binder et al. (Angew. Chem., 127 (2015) 13461-13465).
The disclosures of Liu et al. and Binder et al. are hereby
incorporated by reference.
[0027] Any atomic ratio can be used for the metal component of the
metal oxide in the ternary mixed metal oxide. Suitable atomic
ratios can be precisely, about, at least, up to, or less than 10,
9, 8, 7, 6, 5, 4, 3, 2 or 1, independently for each metal
component, or an atomic ratio within a range bounded by any two of
the foregoing values. For example, in one embodiment, the copper
oxide-cobalt oxide-cerium oxide can have an atomic ratio of 1:5:5
for Cu:Co:Ce.
[0028] The ternary mixed metal oxide can be synthesized by any
method known to those skilled in the art. See for example, the
method disclosed in Lie et al. (Applied Catalysis A: General, 451
(2013) 282-288) for the synthesis of the ternary mixed metal oxide,
copper oxide-cobalt oxide-cerium oxide
[0029] The second component of the composite catalyst comprises
platinum group metals (PGMs). Platinum group metals useful in the
composite catalyst of the present invention include Platinum,
Osmium, Iridium, Ruthenium, Rhodium, and Palladium. Such platinum
group metals fall in groups 8, 9, and 10 and period 5 and 6 of the
periodic table. The platinum group metal can be any of these metals
or any combination of platinum group metals.
[0030] In one embodiment, when the second component of the
composite catalyst is an active PGM of significant cost, the active
PGM is commonly supported on a high surface area metal oxide
support. In this embodiment, the active PGM is dispersed across the
metal oxide support to form a multitude of high surface area
particles for the active metal to efficiently catalyze chemical
reactions based on the pollutant species chemisorbing on the active
metal surface. The metal oxide support may be alumina, ceria,
zirconia, silica, or other metal oxides known to those skilled in
the art. In effect, the support metal oxide serves to preserve a
durable dispersion of active metal sites for the catalytic
reactions to occur.
[0031] In one embodiment, the platinum group metals are nanosized.
The term "nanosized" as used herein refers to particles having a
diameter in the nanosize range. The nanosized particles generally
have a size of no more than about 1000 nm. In different
embodiments, the nanosized objects have a size of precisely, about,
at least, up to, or less than 900 nm, 800 nm, 700 nm, 600 nm, 500
nm, 450 nm, 400 nm, 350 nm, 300 nm, 250 nm, 200 nm, 150 nm, 100 nm,
90 nm, 50 nm, 40 nm, 30 nm, 20 nm, 10 nm, 5 nm, 4 nm, 3 nm, 2 nm,
or 1 nm, or a size within a range bounded by any two of the
foregoing values. As used herein, the term "about" generally
indicates within .+-.0.5, 1, 2, 5, or 10% of the indicated value
(for example, "about 50 nm" can mean 50 nm.+-.2%, which indicates
50.+-.1 nm or 49-51 nm). For example, the nanosized particles
useful in the present invention can have a diameter from 1-100 nm,
5-90 nm, 10-50 nm, etc.
[0032] The first component and the second component of the
composite catalyst of the invention can be combined by any method
known to those skilled in the art. For example, the composite
catalyst can be a physical mixture of the first component and the
second component. Physical mixtures can be made by any method known
in the art. Having the first component in intimate contact with the
second component is not necessary to achieve the improved
performance; thus, there are large numbers of options available to
combine the first and second components to achieve the desired
improved performance provided the first and second components are
as described.
[0033] For example, in another embodiment, the first component and
the second component can be in series with respect to the process
flow of the pollutant containing stream, with either the first
component or the second component being first in the series. For
example, the first component (ternary mixed metal oxide) can be
placed upstream of the second component (PGM-based catalyst) so
that the first component can oxidize CO at low temperatures so that
the second component can be more effective at oxidizing HCs in the
stream once CO is removed from the stream. Here removal of the CO
species from the stream enables the PGM-based catalyst to oxidize
HCs at lower temperatures since CO is not present to chemisorb onto
the PGM surface and inhibit HC reactions on that surface.
[0034] In yet another embodiment, the active PGM portion of the
second component is affixed directly on the surface of the first
component (ternary mixed metal oxide) surface to form an intimate
contact between the ternary mixed metal oxide and PGM materials. In
this manner, the PGM metal is very closely positioned to the
ternary mixed metal oxide sites on a nanometer and atomic scale
such that adsorbed pollutant species can readily translate between
the PGM and ternary mixed metal oxide active sites. Such increased
mobility of pollutant or intermediate reaction product species
between the catalytically active PGM and ternary mixed metal oxide
sites can facilitate oxidation of the pollutant species at the
lowest temperature or energy state available by both PGM and
ternary mixed metal oxide sites.
[0035] The first and second components can be combined in the range
of ternary mixed metal oxide making up between 1% and 99% of the
composite catalyst and catalyst with platinum group metal between
99% and 1% of the composite catalyst. In different embodiments, the
composite catalyst has a percentage of ternary mixed metal oxide
precisely, about, at least, up to, or less than 90%, 80%, 70%, 60%,
50%, 40%, 30%, 20%, 10%, or a percentage of ternary mixed metal
oxide particles within a range bounded by any two of the foregoing
values. In other embodiments, the composite catalyst has a
percentage of platinum group metal containing catalyst precisely,
about, at least, up to, or less than 90%, 80%, 70%, 60%, 50%, 40%,
30%, 20%, 10%, or a percentage of platinum group metal containing
catalyst within a range bounded by any two of the foregoing values.
In one embodiment, the ternary mixed metal oxide will make up
between 40% and 60% of the composite catalyst and the platinum
group metal containing catalyst will make up between 60% and 40% of
the composite catalyst. In the platinum group metal catalyst
component embodiment where the platinum group metals are supported
on a metal oxide different form the ternary mixed metal oxide
component, the platinum group metal has a percentage of about, at
least, up to, or less than 10%, 5%, 2%, 1%, 0.5%, 0.2%, 0.1%,
0.05%, 0.02%, 0.01%, 0.005%, 0.002%, 0.001% or a percentage of
platinum group metal within a range bounded by any two of the
foregoing values. In the composite catalyst embodiment where the
platinum group metal is supported directly on the ternary mixed
metal oxide component, the platinum group metal has a percentage of
about, at least, up to, or less than 10%, 5%, 2%, 1%, 0.5%, 0.2%,
0.1%, 0.05%, 0.02%, 0.01%, 0.005%, 0.002%, 0.001% or a percentage
of platinum group metal within a range bounded by any two of the
foregoing values.
[0036] It is the combination of the first and second components of
the composite catalyst that created unexpected results indicating a
synergistic combination that results in the combination of the
materials creating a composite catalyst with superior low
temperature performance over either of the components individually.
For example, the composite catalysts of the present invention are
capable of catalyzing the oxidation of CO to CO.sub.2 at low
temperatures, such as at, or, around 150.degree. C. In addition,
surprisingly, the composite catalyst gave higher hydrocarbon
oxidation efficiencies at lower temperatures than either the
ternary mixed metal oxide catalyst or platinum group metal catalyst
alone. Thus, useful composite catalysts with improved low
temperature oxidation performance can be used in many applications,
including automotive exhaust emission control.
[0037] The composite catalyst of the invention can be used in any
system in which it is beneficial to oxidize carbon monoxide,
hydrocarbons, nitric oxide or any combination of these species. In
one embodiment, the composite catalyst is an exhaust system. Such
exhaust systems can be in an engine. For example, the engine can be
in a motor vehicle, an airplane, etc. Or, the engine may be
stationary and operate for the purpose of producing
electricity.
[0038] In another embodiment, the composite catalyst is in an
emission control system. The composite catalyst can be used in
industrial processes that generate CO, hydrocarbons, and other
pollutants including power generation facilities and heating
systems.
EXAMPLES
Example 1
[0039] A ternary mixed metal oxide catalyst composed of CuO,
Co.sub.3O.sub.4, and CeO.sub.2 was synthesized by precipitation.
The molar ratios (Cu:Co:Ce) used in the catalyst was 1:5:5, and the
catalyst will be referred to as "CCC". (CCC), 1:0:10 (CuCo), 1:10:0
(CuCe), and 0:5:5 (CoCe). During synthesis of the CCC catalyst,
0.2416 g (1 mmol) of copper nitrate trihydrate
(Cu(NO.sub.3).sub.2.3H.sub.2O, Aldrich) and appropriate amounts of
cobalt chloride hexahydrate (CoCl.sub.2.6H.sub.2O, Aldrich) and
cerium nitrate hexahydrate (Ce(NO.sub.3).sub.2.6H.sub.2O, Aldrich)
were simultaneously added to 100 mL deionized water and dissolved
at room temperature. Next, 100 mL NaOH solution (0.375 M) was added
to the solution dropwise under vigorous stirring. After
approximately 30 min the precipitate was filtered by vacuum
filtration. The obtained product was washed with H.sub.2O followed
by ethanol and allowed to dry at room temperature until it flaked
easily from the filter paper, followed by further drying at
60.degree. C. in a vacuum oven. Calcination at 600.degree. C.
(1.degree. C./min rate) in air resulted in the as-synthesized
catalyst.
[0040] A Pt-based catalyst was synthesized by co-precipitation of a
Pt aqueous solution on a high surface area .gamma.-Al.sub.2O.sub.3
(Aldrich). The Pt loading was 1% by weight. The catalyst was
calcined at 600.degree. C. (1.degree. C./min rate) in air.
[0041] A physical mixture of the CCC and Pt/Al.sub.2O.sub.3
catalysts was prepared by combining equal mass of the CCC and
Pt/Al.sub.2O.sub.3 catalysts. In this manner, the Pt loading of the
physical mixture was half of the Pt in an equal mass of the
Pt/Al.sub.2O.sub.3 catalyst.
[0042] The CCC, Pt/Al.sub.2O.sub.3, and physical mixture of both
catalysts (CCC+ Pt/Al.sub.2O.sub.3) were evaluated in a quartz
powder reactor under simulated exhaust conditions. Temperature and
flow were controlled by a furnace and mass flow controllers,
respectively; the space velocity (ratio of gas flow to catalyst
volume) of flow was controlled to 150,000/hr. Quartz wool was
placed upstream and downstream of the catalyst powder to fix the
catalyst position in gas flow stream. The simulated exhaust mixture
consisted of 1% CO, 500 ppm C.sub.3H.sub.6, 500 ppm C.sub.3H.sub.8,
500 ppm NO, 10% O.sub.2, and 5% H.sub.2O in a Ar balance. CO.sub.2
is also common to exhaust streams but was not added to the
experimental gas to enable monitoring of CO.sub.2 as a product of
the oxidation reactions for the purpose of verifying complete
oxidation of the CO and hydrocarbon constituents. H.sub.2O was
added via flow of the gases through liquid H.sub.2O such that
H.sub.2O vapor entered the gas stream.
[0043] The oxidation efficiency of the CO, C.sub.3H.sub.6, and
C.sub.3H.sub.8 constituents of the gas stream are shown in FIGS.
1A, 1B, and 1C, respectively, as a function of inlet gas
temperature for the CCC, Pt/Al.sub.2O.sub.3, and CCC+
Pt/Al.sub.2O.sub.3 catalysts. For all data, the conversion of the
pollutant species was achieved via oxidation to CO.sub.2 and
H.sub.2O products. As observed in the CO data (FIG. 1A), the CCC
catalyst showed the lowest temperature of oxidation of CO, and the
Pt/Al.sub.2O.sub.3 catalyst required a temperature
.about.80.degree. C. higher for similar oxidation efficiencies to
occur. The CCC+ Pt/Al.sub.2O.sub.3 composite catalyst achieved CO
oxidation at almost the same temperature as the CCC catalyst alone
(only 5-10.degree. C. higher temperature). For the oxidation of
C.sub.3H.sub.6 (FIG. 1B), surprisingly, the CCC+ Pt/Al.sub.2O.sub.3
composite catalyst achieved oxidation of C.sub.3H.sub.6 at
temperatures significantly lower than either the Pt/Al.sub.2O.sub.3
or CCC catalysts alone. The CCC+ Pt/Al.sub.2O.sub.3 catalyst
oxidizes C.sub.3H.sub.6 at .about.40.degree. C. lower temperatures
than the Pt/Al.sub.2O.sub.3 catalyst and at -150.degree. C. lower
temperatures than the CCC catalyst. Since the composite catalyst
has only half of the Pt content as the Pt/Al.sub.2O.sub.3 catalyst
and the CCC catalyst is only effective for C.sub.3H.sub.6 oxidation
at much higher temperatures, this result clearly shows a
synergistic advantage obtained by the combination of materials in
the composite CCC+ Pt/Al.sub.2O.sub.3 catalyst.
[0044] The oxidation of C.sub.3H.sub.8 (FIG. 1C) shows relatively
high temperatures are required for the oxidation of C.sub.3H.sub.8
by all three catalysts. Thus, if neither component in the composite
CCC+ Pt/Al.sub.2O.sub.3 catalyst are active for C.sub.3H.sub.8
conversion, little improvement in oxidation is observed for the
CCC+ Pt/Al.sub.2O.sub.3 catalyst. It is important to note that
C.sub.3H.sub.8 is known to be more difficult to oxidize
catalytically than C.sub.3H.sub.6 due to the higher concentration
of C-H bonds. Considering all three pollutant species of interest
in the example (CO, C.sub.3H.sub.6, and C.sub.3H.sub.8), the
composite CCC+ Pt/Al.sub.2O.sub.3 catalyst gives the best overall
low temperature oxidation performance for all three species and
enables improved performance of the Pt-based catalyst at half the
Pt content which demonstrates significant cost reduction.
Example 2
[0045] A ternary mixed metal oxide catalyst composed of CuO,
Co.sub.3O.sub.4, and CeO.sub.2 (CCC) was synthesized as described
in Example 1 and compared with a Pd-based catalyst in reactor
studies similar to the study described in Example 1. The Pd-based
catalyst was created with a SiO.sub.2 and ZrO.sub.2 high surface
area support. During catalyst synthesis, amorphous silica gel
(Davisil Grade 635, Aldrich) was used as a support, and ZrO.sub.2
was incorporated on the SiO.sub.2 surface. SiO.sub.2 was first
dehydrated with anhydrous ethanol (200 proof, anhydrous,
.gtoreq.99.5%, Aldrich) and reacted at 80.degree. C. for 3 h with
zirconium(IV) n-propoxide (70% w/w in n-propanol, Alfa Aesar)
dissolved in ethanol. ZrO.sub.2-incorporated SiO.sub.2 were
obtained by removing the non-reacted precursors through washing
with ethanol followed by drying at 100.degree. C. and calcining at
500.degree. C. for 2 h. Palladium (II) nitrate solution (Pd
12.about.16 w/w, Alfa Aesar) was impregnated on
ZrO.sub.2--SiO.sub.2 supports by incipient wetness method to 1 wt %
Pd loading. After the impregnation, the catalysts were dried at
100.degree. C. in air and reduced in a flow of 10% H.sub.2 in Ar at
500.degree. C. for 2 h. The catalyst was then calcined at
600.degree. C. in air.
[0046] The CCC component was compared with the
Pd/ZrO.sub.2--SiO.sub.2 catalyst in a simulated exhaust stream
containing 0.4% CO, 500 ppm NO, 10% O.sub.2, and 5% H.sub.2O in an
Ar balance. Experiments were conducted with 0% C.sub.3H.sub.6 and
with 0.1% C.sub.3H.sub.6 added to the stream, and the oxidation
efficiency of CO was monitored as a function of inlet gas
temperature. The resulting data (FIG. 2) shows CO oxidation
efficiency in the presence of C.sub.3H.sub.6 (dashed line and "x"
icons) as well as the CO oxidation efficiency without
C.sub.3H.sub.6 present (solid line) for both the CCC and
Pd/ZrO.sub.2--SiO.sub.2 catalysts. For the Pd-based catalyst, the
addition of C.sub.3H.sub.6 to the exhaust stream greatly impacts
the CO oxidation negatively as higher inlet gas temperatures are
required to oxidize CO in the presence of C.sub.3H.sub.6. Such data
is typical of the inhibition of hydrocarbon (HC) species on the
reactivity for CO oxidation by platinum group metal catalysts.
While a Pd-based catalyst is shown here, the effect has been
observed on Pt-based catalysts, catalysts with mixtures of Pt and
Pd, and catalysts with other platinum group metals and mixtures
thereof. In contrast, the CCC catalyst shows virtually no
difference in the CO oxidation efficiency as a function of
temperature with or without the presence of C.sub.3H.sub.6. The
lack of inhibition of hydrocarbon species on the CO oxidation
process on the CCC catalyst is a unique property that may explain
the improved performance by the composite CCC+ Pt/Al.sub.2O.sub.3
catalyst in Example 1 above.
Example 3
[0047] The adsorption of CO and hydrocarbon species onto the CCC
and Pd/ZrO.sub.2--SiO.sub.2 catalysts described in Example 2 above
was characterized with Diffuse Reflectance Infrared Fourier
Transform Spectroscopy (DRIFTS) as shown in FIG. 3. Here the
catalysts were first exposed to CO so that CO could saturate any
adsorption sites on the catalyst surface. Then, C.sub.3H.sub.6 was
introduced into the gas stream flowing over the catalysts, and
DRIFTS spectra were monitored over time during C.sub.3H.sub.6
exposure. Details of the DRIFTS measurements performed using a
Digilab FTS 7000 series FTIR spectrometer equipped with a Praying
Mantis DRIFTS apparatus as follows: The catalyst bed was first
cleaned by heating to 400.degree. C. in O.sub.2/Ar. DRIFTS spectra
were taken at a temperature within a region of 5-10% CO oxidation
as determined by reactor analysis. After the cleaning step, the bed
was cooled to the analysis temperature, and a clean background was
taken in 10% O.sub.2/Ar. [CO]=0.4% was then introduced into the
stream and a spectrum taken after 30 min of exposure.
[C.sub.3H.sub.6]=0.1% was then added and a spectrum was taken
immediately up introduction followed by additional spectra at 10,
20, and 30 min exposure times. Spectra were obtained at 2 cm.sup.-1
resolution with 64 scans averaged.
[0048] The resulting DRIFTS spectra for the CCC (FIG. 3A) and
Pd/ZrO.sub.2--SiO.sub.2 (FIG. 3B) catalysts show dramatic
differences in the surface species occurring during C.sub.3H.sub.6
exposure. The CCC spectra show very little change in the 2800-3200
cm.sup.-1 range which is commonly associated with hydrocarbon
adsorption onto the surface; this indicates hydrocarbons do not
readily adsorb onto the CCC catalyst surface. In contrast, the Pd
catalyst shows strong adsorption bands in the 2800-3200 cm.sup.-1
region that occur once the catalyst is exposed to C.sub.3H.sub.6.
Thus, the Pd-based catalyst readily adsorbs the C.sub.3H.sub.6. In
addition, comparison of the wavenumber range associated with
CO-bonding (2105-2111 cm.sup.-1) shows that the Cu.sup.+--CO bond
is essentially not affected by C.sub.3H.sub.6 exposure to the CCC
catalyst, but the Pd/ZrO.sub.2--SiO.sub.2 catalyst shows a dramatic
shift between Pd.sup.2+--CO and Pd.sup.+-CO bonds once
C.sub.3H.sub.6 exposure occurs.
[0049] These data provide evidence to support the data shown in
Examples 1 and 2. The CCC catalyst can oxidize CO without
inhibition from the presence of hydrocarbons since hydrocarbons are
not strongly adsorbed onto the CCC surface. In contrast, the
Pd-based catalyst readily adsorbs hydrocarbons which cause
inhibition of the CO oxidation process via competition for
adsorption on the active Pd site, but once the platinum group metal
catalyst is combined with the CCC catalyst, CO oxidation can occur
on the CCC catalyst even in the presence of hydrocarbons.
Subsequently, the resulting exhaust stream contains only the
remaining hydrocarbon species that the CCC did not control but can
be oxidized readily by the (CO-free) platinum group metal
catalyst.
Example 4
[0050] The CCC catalyst was analyzed with scanning transmission
electron microscopy (STEM) including energy dispersive x-ray (EDX)
analysis of atomic composition. The resulting data images are shown
in FIG. 4 where the black bar denotes a scale of 100 nm. The data
show that the Ce-, Co-, and Cu-oxide phases are mixed well and form
a composite mixed metal oxide particle agglomeration as shown in
the raw STEM image (FIG. 4D). Also, based observation of the EDX
data for Ce (FIG. 4A), Co (FIG. 4B), and Cu (FIG. 4C), the Cu
appears to be the most uniform component and occurs in association
with both Ce and Co phases.
[0051] Binary combinations of the Ce-, Co-, and Cu-oxides were also
prepared and studied in a reactor under simulated exhaust
conditions as described above. Results for the oxidation efficiency
of CO and C.sub.3H.sub.6 over the binary mixtures as compared with
the ternary mixed metal oxide CCC catalyst are shown in FIG. 5. The
CO data (FIG. 5A) shows that the ternary mixed metal oxide catalyst
enables oxidation of CO at much lower temperatures than any of the
other binary combinations of metal oxides. The C.sub.3H.sub.6 data
(FIG. 5B) shows that C.sub.3H.sub.6 oxidation is equivalent for any
of the ternary or binary combinations that contain Co and Ce
oxides, but the binary combination of Cu- and Ce-oxides requires a
higher temperature for C.sub.3H.sub.6 oxidation. Overall, the
ternary mixed metal oxide catalyst (CCC) gives the best combined
oxidation performance for CO and C.sub.3H.sub.6.
Example 5
[0052] As described above, the composite catalyst containing both
the ternary mixed metal oxide and platinum group metal based
catalysts can be combined by various methods to achieve improved
oxidation for CO and hydrocarbons at low temperatures. FIG. 6 shows
C.sub.3H.sub.6 oxidation efficiency as a function of temperature
for different methods of combining the ternary mixed metal oxide
and platinum group metal catalyst components. Here the ternary
mixed metal oxide component is represented by CCC, and the platinum
group metal catalyst component is represented by the
Pt/Al.sub.2O.sub.3 catalyst. Both the CCC and Pt/Al.sub.2O.sub.3
are as described in Example 1. Experiments were conducted in a
reactor as described above in Example 1 with a simulated exhaust
stream containing 1% CO, 500 ppm C.sub.3H.sub.6, 500 ppm
C.sub.3H.sub.8, 500 ppm NO, 10% O.sub.2, and 5% H.sub.2O in a Ar
balance.
[0053] The C.sub.3H.sub.6 oxidation efficiency of the CCC and
Pt/Al.sub.2O.sub.3 components alone are shown in FIG. 6 with the
Pt/Al.sub.2O.sub.3 catalyst demonstrating lower temperature
oxidation of C.sub.3H.sub.6. Performance of the three methods for
combining the CCC and Pt/Al.sub.2O.sub.3 catalysts are as follows.
A physical mixture of the CCC and Pt/Al.sub.2O.sub.3 catalysts at a
50:50 ratio by weight (CCC+PA) gives the lowest temperature for
oxidation of C.sub.3H.sub.6. Combining the CCC and
Pt/Al.sub.2O.sub.3 components in series with the CCC catalyst
upstream of the Pt/Al.sub.2O.sub.3 catalyst (CCC.fwdarw.PA) gives
the second best performance and lower temperature oxidation of
C.sub.3H.sub.6 as compared with the Pt/Al.sub.2O.sub.3 catalyst.
Finally, direct precipitation of Pt onto the CCC catalyst with a
total Pt loading of 0.5% by weight (Pt/CCC) results in oxidation of
C.sub.3H.sub.6 at temperatures between those exhibited by the Pt
and CCC components individually. Considering that all of the
composite catalyst combinations CCC+PA, CCC.fwdarw.PA, and Pt/CCC
have nominally 50% of the Pt as the Pt/Al.sub.2O.sub.3 catalyst,
the data demonstrate improved catalyst utility of the composite
ternary mixed metal oxide and platinum group metal catalyst as
compared to the Pt/Al.sub.2O.sub.3 and CCC catalysts
individually.
* * * * *