U.S. patent application number 14/669669 was filed with the patent office on 2015-07-16 for palladium solid solution catayst and methods of making.
This patent application is currently assigned to CLEAN DIESEL TECHNOLOGIES, INC.. The applicant listed for this patent is Stephen J. Golden, Randal Hatfield, Johnny T. Ngo, Jason D. Pless. Invention is credited to Stephen J. Golden, Randal Hatfield, Johnny T. Ngo, Jason D. Pless.
Application Number | 20150196902 14/669669 |
Document ID | / |
Family ID | 47668918 |
Filed Date | 2015-07-16 |
United States Patent
Application |
20150196902 |
Kind Code |
A1 |
Golden; Stephen J. ; et
al. |
July 16, 2015 |
PALLADIUM SOLID SOLUTION CATAYST AND METHODS OF MAKING
Abstract
Disclosed are three-way catalysts that are able to
simultaneously convert nitrogen oxides, carbon monoxide, and
hydrocarbons in exhaust gas emissions into less toxic compounds.
Also disclosed are three-way catalyst formulations comprising
palladium (Pd)-containing oxygen storage materials. In some
embodiments, the three-way catalyst formulations of the invention
do not contain rhodium. Further disclosed are improved methods for
making Pd-containing oxygen storage materials. The relates to
methods of making and using three-way catalyst formulations of the
invention.
Inventors: |
Golden; Stephen J.; (Santa
Barbara, CA) ; Hatfield; Randal; (Oxnard, CA)
; Pless; Jason D.; (Pottstown, PA) ; Ngo; Johnny
T.; (Oxnard, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Golden; Stephen J.
Hatfield; Randal
Pless; Jason D.
Ngo; Johnny T. |
Santa Barbara
Oxnard
Pottstown
Oxnard |
CA
CA
PA
CA |
US
US
US
US |
|
|
Assignee: |
CLEAN DIESEL TECHNOLOGIES,
INC.
Oxnard
CA
|
Family ID: |
47668918 |
Appl. No.: |
14/669669 |
Filed: |
March 26, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13569724 |
Aug 8, 2012 |
9012353 |
|
|
14669669 |
|
|
|
|
61521835 |
Aug 10, 2011 |
|
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Current U.S.
Class: |
423/213.2 ;
422/180; 502/304 |
Current CPC
Class: |
B01D 2255/2065 20130101;
B01J 37/08 20130101; B01J 23/63 20130101; B01D 2255/407 20130101;
B01D 2255/20753 20130101; B01D 2255/1025 20130101; B01J 23/002
20130101; B01D 2255/2063 20130101; B01D 53/945 20130101; B01D
2255/1023 20130101; B01J 35/0073 20130101; B01J 37/0201 20130101;
B01J 35/0006 20130101; B01J 23/83 20130101; B01J 37/0036 20130101;
B01J 37/0244 20130101; B01J 23/44 20130101; B01J 37/0215 20130101;
B01D 2255/20715 20130101; B01D 2255/908 20130101; B01J 35/002
20130101; B01J 37/04 20130101; B01D 2255/2073 20130101; F01N
2510/0684 20130101; B01D 2255/204 20130101; F01N 3/101 20130101;
B01J 23/34 20130101; B01J 2523/00 20130101; B01D 2255/206 20130101;
B01D 2255/2061 20130101; B01D 2255/2066 20130101; B01D 2255/2068
20130101; Y02T 10/22 20130101; B01D 2255/20761 20130101; F01N
2570/16 20130101; Y02T 10/12 20130101; B01J 37/038 20130101; B01J
2523/00 20130101; B01J 2523/36 20130101; B01J 2523/3712 20130101;
B01J 2523/3725 20130101; B01J 2523/48 20130101 |
International
Class: |
B01J 37/08 20060101
B01J037/08; B01J 23/63 20060101 B01J023/63; B01D 53/94 20060101
B01D053/94; B01J 37/02 20060101 B01J037/02; B01J 37/04 20060101
B01J037/04 |
Claims
1. (canceled)
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. (canceled)
7. (canceled)
8. (canceled)
9. (canceled)
10. (canceled)
11. (canceled)
12. (canceled)
13. A method of making the oxygen storage material (OSM) comprising
a metal oxide doped with at least one transition metal, wherein
said transition metal and OSM are present as a solid solution,
comprising: 1) adding an amount of transition metal salt to an
aqueous slurry of milled OSM; and 2) adding an amount of base to
generate an IWCP-OSM slurry.
14. A method of making a catalyst composition comprising an oxygen
storage material (OSM) prepared as in claim 13, comprising: 1)
generating an IWCP-OSM slurry by: a) adding an amount of transition
metal salt to an aqueous slurry of milled OSM; and b) adding an
amount of base to generate an IWCP-OSM slurry; 2) generating a
support oxide mixture by: a) milling an amount of support oxide
with acetic acid; b) adding an amount of BaCO.sub.3 or CaCO.sub.3
and stirring to generate a support oxide mixture; 3) adding said
support oxide mixture of 2) to said IWCP-OSM slurry of 1) and
coating the resulting composition on to a washcoat; and 4)
calcining the resulting mixture of 3) to yield a catalyst
composition.
15. A method of increasing oxygen flow through a catalyst system by
utilizing an oxygen storage material (OSM) prepared as in claim 13
comprising a metal oxide doped with at least one transition metal,
wherein said OSM is present in the washcoat, overcoat, or both, and
wherein said transition metal and OSM are present as a solid
solution.
16. A method of increasing the oxygen storage capacity of a
catalyst system by utilizing an oxygen storage material (OSM)
prepared as in claim 13 comprising a metal oxide doped with at
least one transition metal, wherein said OSM is present in the
washcoat, overcoat, or both, and wherein said transition metal and
OSM are present as a solid solution.
17. A method of improving the lifetime of a platinum group metal
(PGM) catalyst present in a catalyst system by utilizing an oxygen
storage material (OSM) prepared as in claim 13 comprising a metal
oxide doped with at least one transition metal, wherein said OSM is
present in the washcoat, overcoat, or both, and wherein said
transition metal and OSM are present as a solid solution.
18. A method of improving the light-off performance of a catalyst
system by utilizing an oxygen storage material (OSM) prepared as in
claim 13 comprising a metal oxide doped with at least one
transition metal, wherein said OSM is present in the washcoat,
overcoat, or both, and wherein said transition metal and OSM are
present as a solid solution.
19. A method of reducing the amount of Rh present in a catalyst
system while maintaining catalyst efficiency by utilizing an oxygen
storage material (OSM) prepared as in claim 13 comprising a metal
oxide doped with at least one transition metal, wherein said OSM is
present in the washcoat, overcoat, or both, and wherein said
transition metal and OSM are present as a solid solution.
20. A method of simultaneously converting a) nitrogen oxides to
nitrogen and oxygen; b) carbon monoxide to carbon dioxide; and c)
hydrocarbons to carbon dioxide and water present in exhaust gas
emissions, comprising contacting said gas emissions with the
catalyst system comprising a substrate and a washcoat, wherein said
washcoat comprises an oxygen storage material (OSM) prepared as in
claim 13.
21. A catalytic convertor system comprising a catalyst system
comprising: a substrate and a washcoat, wherein said washcoat
comprises an oxygen storage material (OSM), doped with at least one
transition metal prepared as in claim 13, wherein said transition
metal and said OSM are present as a solid solution.
22. A close coupled catalytic converter comprising the oxygen
storage material (OSM) prepared as in claim 13 comprising a metal
oxide doped with at least one transition metal, wherein said
transition metal and OSM are present as a solid solution.
23. (canceled)
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application No. 61/521,835, filed Aug. 10, 2011, which is
incorporated herein by reference in its entirety.
TECHNICAL FIELD OF INVENTION
[0002] The invention relates generally to three-way catalysts that
are able to simultaneously convert nitrogen oxides, carbon
monoxide, and hydrocarbons in exhaust gas emissions into less toxic
compounds. The invention relates specifically to three-way catalyst
formulations comprising palladium (Pd)-containing oxygen storage
materials. In some embodiments, the three-way catalyst formulations
of the invention do not contain rhodium (Rh). The invention further
relates to improved methods for making Pd-containing oxygen storage
materials. Furthermore, the present invention relates to methods of
making and using three-way catalyst formulations of the
invention.
BACKGROUND OF THE INVENTION
[0003] Nitrogen oxides, carbon monoxide, and hydrocarbons are toxic
and environmentally damaging byproducts found in the exhaust gas
from internal combustion engines. Methods of catalytically
converting nitrogen oxides, carbon monoxide, and hydrocarbons into
less harmful compounds include the simultaneous conversion of these
by-products (i.e., "three-way conversion" or "TWC"). Specifically,
nitrogen oxides are converted to nitrogen and oxygen, carbon
monoxide is converted to carbon dioxide, and hydrocarbons are
converted to carbon dioxide and water.
[0004] It has generally been found that TWC significantly increases
the efficiency of conversion of these pollutants and, thus, aids in
meeting emission standards for automobiles and other vehicles. In
order to achieve an efficient three-way conversion of the toxic
components in the exhaust gas, conventional TWC contain large
quantities of precious metals, such as Pd (Palladium), Pt
(Platinum) and Rh (Rhodium), dispersed on suitable oxide carriers.
Because Rh-containing catalysts demonstrate a very high activity
for the conversion of NO.sub.x, Rh is typically considered to be an
essential component of the TWC system. As NO emission standards
tighten and Rh becomes scarce (and, thus, more expensive), there is
an increasing need for new TWC catalyst compositions which require
lower amounts of precious metal catalysts and maintain efficient
TWC of exhaust byproducts.
[0005] Thus, there remains a need for TWC catalyst formulations
that do not contain Rh and that exhibit efficient TWC of exhaust
byproducts. There also remains a need for efficient methods of
producing such TWC catalyst formulations.
SUMMARY OF THE INVENTION
[0006] In some embodiments, the present invention relates to an
oxygen storage material (OSM) comprising a metal oxide doped with
at least one transition metal, wherein the transition metal and OSM
are present as a solid solution. In some embodiments, the OSM is a
Ce-based oxygen storage material.
[0007] The OSM may be doped with a particular amount of the
transition metal. For example, the OSM may be doped with 0.5-10% of
the transition metal. In some embodiments, the OSM is doped with
about 2%, 5% or 10% of the transition metal. In a particular
embodiment, the OSM is doped with about 2% of the transition metal.
In other embodiments, the OSM is doped with about 0.5-4% of the
transition metal. In yet other embodiments, the OSM is doped with
about 1-2.5% of the transition metal. In particular embodiments,
the OSM may be doped with up to about 2% of the transition metal.
In other particular embodiments, the OSM is doped with about 2,
2.21 or 4.08% of the transition metal.
[0008] The OSM may comprise about 5-100 g/ft.sup.3, 5-50
g/ft.sup.3, or 5-20 g/ft.sup.3 of the transition metal. In some
embodiments, the OSM comprises about 5-20 g/ft.sup.3 of the
transition metal.
[0009] A variety of transition metals may be used in the OSMs of
the present invention. For example, the transition metal may be Pd,
Cu, Mn or Ni. In some embodiments, the transition metal is Pd.
[0010] In particular embodiments, the OSM is a SS Pd-IWCP OSM, as
described herein.
[0011] In another aspect, the present invention relates to a
washcoat comprising the OSM described above. In some embodiments,
the washcoat further comprises a compound which retards the
poisoning of a catalyst, such as barium. Barium can be present in
the washcoat at about 19-21, 18-22, 17-23, 16-24, 15-25, 29-31,
28-32, 27-33, 26-34, or 25-35 g/L. In some embodiments, the barium
is present in the washcoat at a concentration of about 20g/L or
about 30g/L. The washcoat may also comprise an amount of
La--Al.sub.2O.sub.3. In some embodiments, the La--Al.sub.2O.sub.3
constitutes about 9-11%, 8-12%, 7-13%, 6-14%, or 5-15% of the
washcoat by weight. In other embodiments, the La--Al.sub.2O.sub.3
constitutes about 10% of the washcoat by weight.
[0012] In yet another aspect, the present invention relates to an
overcoat comprising the OSM described above. In some embodiments,
the overcoat further comprises a compound which retards the
poisoning of a catalyst, such as barium. Barium can be present in
the overcoat at about 19-21, 18-22, 17-23, 16-24, 15-25, 29-31,
28-32, 27-33, 26-34, or 25-35 g/L. In some embodiments, the barium
is present in the overcoat at a concentration of about 20 g/L or
about 30 g/L. The overcoat may also comprise an amount of
La--Al.sub.2O.sub.3. In some embodiments, the La--Al.sub.2O.sub.3
constitutes about 9-11%, 8-12%, 7-13%, 6-14%, or 5-15% of the
overcoat by weight. In other embodiments, the La--Al.sub.2O.sub.3
constitutes about 10% of the overcoat by weight.
[0013] The present invention further relates to a catalyst system
comprising: a substrate and a washcoat, wherein the washcoat
comprises an OSM, and wherein the OSM is as described above. In
other embodiments, the present invention relates to a catalyst
system comprising: a substrate, a washcoat, and an overcoat,
wherein the washcoat comprises an OSM, wherein the OSM is as
described above, and the overcoat comprises a support oxide, an OSM
and a metal catalyst. In addition, the present invention refers to
a catalyst system comprising: a substrate, a washcoat, and an
overcoat, wherein the washcoat comprises a support oxide, an OSM
and a metal catalyst, and the overcoat comprises an OSM as
described above.
[0014] The metal catalyst present in the washcoat may be a platinum
group metal (PGM) catalyst. For example, the PGM catalyst may be
Pd, Pt or Rh. In some embodiments, the PGM catalyst is Pd. The Pd
may be present in the overcoat at a concentration of about 5-100
g/ft.sup.3. In some embodiments, the Pd is present in the overcoat
at a concentration of about 5, 10, 15, 20, 50 or 100 g/ft.sup.3. In
other embodiments, the Pd at is present in the overcoat a
concentration of about 5, 10, or 15 g/ft.sup.3. Similarly, the Pd
may be present in the washcoat at a concentration of about 5-100
g/ft.sup.3. In some embodiments, the Pd is present in the washcoat
at a concentration of about 5, 10, 15, 20, 50 or 100 g/ft.sup.3. In
other embodiments, the Pd at is present in the washcoat a
concentration of about 5, 10, or 15 g/ft.sup.3. In some embodiments
of the catalyst systems, the overcoat comprises Pd at a
concentration of about 5-100 g/ft.sup.3 and the washcoat comprises
Pd at a concentration of about 5-100 g/ft.sup.3. In other
embodiments of the catalyst systems, the overcoat comprises Pd at a
concentration of about 10 g/ft.sup.3 and the washcoat comprises Pd
at a concentration of about 10 g/ft.sup.3. In further embodiments
of the catalyst systems, the overcoat comprises Pd at a
concentration of about 50 g/ft.sup.3 and the washcoat comprises Pd
at a concentration of about 50 g/ft.sup.3. In yet other embodiments
of the catalyst systems, the overcoat comprises less Pd than the
washcoat. In other embodiments of the catalyst systems, the
overcoat comprises Pd at a concentration of about 5 g/ft.sup.3 and
the washcoat comprises Pd at a concentration of about 15
g/ft.sup.3. In some embodiments, the catalyst system is
substantially free of Rh.
[0015] The catalyst systems may contain washcoats comprising the
OSM described above. In addition, the catalyst systems may contain
overcoats comprising the OSM described above.
[0016] The washcoats and overcoats of the catalyst systems may,
independently, further comprise Ca, Sr, Ba or La. In some
embodiments, the washcoats and overcoats of the catalyst systems
independently comprise Ba.
[0017] The present invention also relates to methods of making the
OSMs described above. In particular embodiments, the method is the
IWCP method and comprises the: 1) adding an amount of transition
metal salt to an aqueous slurry of milled OSM; and 2) adding an
amount of base to generate an IWCP-OSM slurry.
[0018] The present invention further relates to methods of making a
catalyst composition comprising the OSMs described above,
comprising: 1) generating an IWCP-OSM slurry by adding an amount of
transition metal salt to an aqueous slurry of milled OSM and then
adding an amount of base to generate an IWCP-OSM slurry; 2)
generating a support oxide mixture by milling an amount of support
oxide with acetic acid and then adding an amount of BaCO.sub.3 or
CaCO.sub.3 and stiffing to generate a support oxide mixture; 3)
adding the support oxide mixture of 2) to the IWCP-OSM slurry of 1)
and coating the resulting composition on to a washcoat; and 4)
calcining the resulting mixture of 3) to yield a catalyst
composition. If needed, the IWCP process may be repeated multiple
times on a substrate.
[0019] In some embodiments of the methods above, the base used is
tetraethylammonium hydroxide, tetramethylammonium hydroxide,
tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, BaO,
Ba(OH).sub.2, BaCO.sub.3, SrO, Sr(OH).sub.2 or SrCO.sub.3. In a
particular embodiment, the base is tetraethylammonium
hydroxide.
[0020] The present invention additionally relates to methods of
making the OSMs described above, comprising: 1) co-milling a
Ce-based oxygen storage material and a transition metal salt; and
2) spraying the resulting mixture of 1) into a furnace. In some
embodiments, the transition metal salt is PdNO.sub.3.
[0021] In some embodiments of the methods above, the base and
transition metal are present in a fixed ratio. In particular
embodiments, the molar ratio of base to transition metal is between
2:1 and 3:1. In some embodiments the molar ratio is 2.5:1 or
2.75:1. In particular embodiments of the methods above, the base is
tetraethylammonium hydroxide and the transition metal is Pd. In
some embodiments, tetraethylammonium hydroxide and Pd are present
in a molar ratio of 2.5:1 or 2.75:1.
[0022] Further methods of the present invention include methods of
reducing toxic exhaust gas emissions comprising contacting the gas
emissions with the catalyst systems described above.
[0023] The present invention also relates to methods of increasing
oxygen flow through a catalyst system by utilizing an OSM described
above, wherein the OSM is present in the washcoat, overcoat, or
both.
[0024] In addition, the present invention relates to methods of
increasing the oxygen storage capacity of a catalyst system by
utilizing an OSM described above, wherein the OSM is present in the
washcoat, overcoat, or both.
[0025] Additional methods encompassed by the invention include
methods of improving the lifetime of a PGM catalyst present in a
catalyst system by utilizing an OSM described above, wherein the
OSM is present in the washcoat, overcoat, or both.
[0026] Further, the invention refers to methods of improving the
light-off performance of a catalyst system by utilizing an OSM
described above, wherein the OSM is present in the washcoat,
overcoat, or both. In some embodiments, the initial exotherm on
contact of the catalyst with CO is increased.
[0027] Other methods include methods for reducing the amount of Rh
present in a catalyst system while maintaining catalyst efficiency
by utilizing an OSM described above, wherein the OSM is present in
the washcoat, overcoat, or both. In some embodiments, the washcoat,
overcoat, or entire catalyst system (washcoat and overcoat) is
substantially free of Rh.
[0028] In addition, the present invention refers to methods of
simultaneously converting a) nitrogen oxides to nitrogen and
oxygen; b) carbon monoxide to carbon dioxide; and c) hydrocarbons
to carbon dioxide and water present in exhaust gas emissions,
comprising contacting the gas emissions with the catalyst systems
described above.
[0029] In another aspect, the present invention refers to a
catalytic convertor system comprising a catalyst system described
above. In some embodiments, the catalytic convertor system
comprises two or more catalytic converters. In further embodiments,
the catalytic convertor system comprises at least one close coupled
catalytic converter. In some embodiments, the close coupled
catalytic converter comprises an OSM described above. In some
embodiments, the catalyst systems described above are present in a
close coupled catalytic converter.
[0030] In a particular aspect, the present invention refers to a
catalyst system comprising a washcoat and an overcoat as follows:
a) an overcoat comprising an OSM and a Pd metal catalyst, wherein
the OSM comprises 30% CeO.sub.2, 60% ZrO.sub.2, 5% Nd.sub.2O.sub.3,
and 5% Pr.sub.6O.sub.11 (% by weight), and the overcoat comprises 5
g/ft.sup.3 of Pd; and b) a washcoat comprising an OSM and a Pd
metal catalyst, wherein the OSM comprises 30% CeO.sub.2, 60%
ZrO.sub.2, 5% Nd.sub.2O.sub.3 and 5% Y.sub.2O.sub.3 (% by weight),
and the washcoat comprises 15 g/ft.sup.3 of Pd.
BRIEF DESCRIPTION OF THE FIGURES
[0031] FIG. 1 is a schematic representation of a TWC catalyst
comprising (1) a substrate, and (2) a washcoat containing at least
one metal catalyst, wherein the washcoat is supported by the
substrate.
[0032] FIG. 2 is a schematic representation of a TWC catalyst
comprising (1) a substrate, (2) a washcoat containing at least one
metal catalyst, wherein the washcoat is supported by the substrate,
and (3) an overcoat containing at least one metal catalyst, wherein
the overcoat is supported by the washcoat.
[0033] FIG. 3 is a schematic representation of a TWC catalyst
comprising (1) a substrate, (2) a washcoat containing at least one
metal catalyst, wherein the washcoat is supported by the substrate,
and (3) an overcoat which is free of metal catalyst.
[0034] FIG. 4 is a schematic representation of a TWC catalyst
comprising (1) a substrate, (2) a washcoat which is free of metal
catalyst and (3) an overcoat containing at least one metal
catalyst, wherein the overcoat is supported by the washcoat.
[0035] FIG. 5 is a schematic representation of a TWC catalyst
system comprising a MPC Pd in the washcoat (lower layer) and
Pd-IWCP OSM in the overcoat (upper layer).
[0036] FIG. 6 is a diagram that illustrates how the presence of Pd
in a solid solution increases the number of oxygen vacancies in the
solid solution and, thus, improves the kinetics of oxygen
diffusion.
[0037] FIG. 7 is a diagram that illustrates the multiplicative
effect on oxygen storage capacity (OSC) of a) increasing the number
of oxygen vacancies; and b) increasing the rate of oxygen
diffusion.
[0038] FIG. 8 is a diagram that illustrates the metastability of
the Pd-solid solution (SS) due to the significant energy required
to drive Pd from the dispersed to the bulk state.
[0039] FIG. 9 is a diagram that illustrates how addition of barium
to the overcoat reduces poisoning of the PGM by phosphorus. Barium
reacts with exhaust phosphorus to form
Ba.sub.3(PO.sub.4).sub.2.
[0040] FIG. 10 is a diagram that illustrates how addition of
La--Al.sub.2O.sub.3 to the OSM reduces sintering and helps to
maintain an open pore structure.
[0041] FIG. 11 illustrates the effects of the amount and kind of
base used in the generation of mixed-metal oxides. Use of the
incorrect base or amount of base can lead to the undesired
formation of Pd, in the form of PdO, agglomerated on the surface of
the OSM (see WCP). Use of the correct base in the correct amount
yields Pd present as a solid solution with the OSM (see IWCP).
[0042] FIG. 12 is a flowchart illustrating the steps of the IWCP
used to generate an overcoat (OC).
[0043] FIG. 13 is a graph of air/fuel ratio versus time during the
early part of US06 cycle. The air/fuel ratio shows major lean
perturbation around 100 seconds.
[0044] FIG. 14 is a graph of NO.sub.x emission (left Y-axis) and
speed (right Y-axis) versus time illustrating the comparative
levels of NO.sub.x emissions of the SS Pd-IWCP OSM and Pd-MPC
catalyst systems.
[0045] FIG. 15 shows graphs of catalyst temperature versus time for
close-coupled (left) and underfloor (right) catalysts and showing
the comparison of increase of temperature with catalyst systems
containing SS Pd-IWCP OSM and Pd-MCP as CC catalysts. The data was
generated using FTP testing. When the SS Pd-IWCP OSM was used in
the CC catalyst, a more rapid increase of temperature was observed
in both the CC and UF catalysts.
[0046] FIG. 16 is a graph of OSC versus temperature that
illustrates that the OSC is influenced by the relative dispersion
of Pd and OSM. OSMs generated using the IWCP (where the Pd is best
dispersed on the surface and throughout the OSM) exhibit the best
OSC.
[0047] FIG. 17 illustrates SEM and X-ray microanalysis of a SS
Pd-OSM generated using the IWCP. As can be seen, the Pd is evenly
dispersed throughout the OSM and correlates with Ce and Zr
concentrations. The scans also indicate that a stable solid
solution of Pd is present in the fluorite phase.
[0048] FIG. 18 illustrates SEM and X-ray microanalysis of a SS
Pd-OSM generated using the WCP. As can be seen, the WCP does not
yield an OSM with Pd present as a solid solution. Rather, the Pd is
present as uneven, large PdO particles on the OSM surface.
[0049] FIG. 19 shows X-ray diffraction plots of 0, 2%, 5% and 10%
Pd in OSM before aging (i.e., as-made). The highlighted peaks are
PdO peaks. As the amount of Pd is increased, the amount of PdO
formed is also increased.
[0050] FIG. 20 shows X-ray diffraction plots of 0, 2%, 5% and 10%
Pd in OSM after aging for 20 hours at 900.degree. C. in 10%
H.sub.2O/N.sub.2. The highlighted peaks are PdO peaks. The data
indicate that, even after aging, only trace amounts of PdO are
present in the 2% Pd sample.
[0051] FIG. 21 shows the calculated Pd concentrations (i.e.,
theoretical or "maximum" values) (as % in solid solution) of fresh
and aged samples of SS Pd-IWCP OSM based on a linear fit of XRD
peak intensity data.
[0052] FIG. 22 is a graph OSC capacity versus Pd content of the
OSM. This graph illustrates that doping of amounts of Pd in excess
of the solid solution limit have a relatively minor impact on the
OSC, presumably because the excess Pd forms bulk Pd or PdO
particles on the surface of the OSM.
[0053] FIG. 23 is graph of lattice parameter versus Pd
concentration of the OSM. The observed lattice parameter
contraction as the Pd concentration is increased is consistent with
the doping of Pd.sup.2+ cations onto the Ce.sup.4+ sites.
[0054] FIG. 24 is a graph that illustrates how CO delay time varies
with the La--Al.sub.2O.sub.3 content of the overcoat. The OSC after
phosphorus aging is improved by adding up to 40%
La--Al.sub.2O.sub.3 to overcoats containing SS Pd-IWCP OSM.
[0055] FIG. 25 is a graph that illustrates the higher thermodynamic
stability of LaPO.sub.4 and Ba.sub.3(PO.sub.4).sub.2 relative to
A1PO.sub.4. This effect contributes to the improved thermodynamic
stability of SS Pd-IWCP OSM overcoat.
[0056] FIG. 25 is a graph that illustrates the higher thermodynamic
stability of LaPO.sub.4 and Ba.sub.3(PO.sub.4).sub.2 relative to
AlPO.sub.4. This effect contributes to the improved thermodynamic
stability of SS Pd-IWCP OSM overcoat.
[0057] FIG. 26 illustrates SEM and X-ray microanalysis of a SS
Pd-OSM generated using the HTP. As can be seen, the Pd is evenly
dispersed throughout the OSM and correlates with Ce and Zr
concentrations. The scans also indicate that a stable solid
solution of Pd is present in the fluorite phase.
[0058] FIG. 27 shows graphs of NO.sub.x emission versus CO emission
(left) and NO.sub.x emission versus hydrocarbon emission (NMOG)
(right). The graphs illustrate the relative FTP performance of a
close coupled catalyst (CCC) comprising a Pd-OSM solid solution
made by a High Temperature Process (HTP) or the Improved Wet
Chemistry Process (IWCP).
DETAILED DESCRIPTION OF THE INVENTION
[0059] In order that the invention herein described may be fully
understood, the following detailed description is set forth.
[0060] Unless defined otherwise, all technical and scientific terms
used herein have the same meaning as those commonly understood by
one of ordinary skill in the art to which this invention belongs.
Although methods and materials similar or equivalent to those
described herein can be used in the practice or testing of the
present invention, suitable methods and materials are described
below. The materials, methods and examples are illustrative only,
and are not intended to be limiting. All publications, patents and
other documents mentioned herein are incorporated by reference in
their entirety.
[0061] Throughout this specification, the word "comprise" or
variations such as "comprises" or "comprising" will be understood
to imply the inclusion of a stated integer or groups of integers
but not the exclusion of any other integer or group of
integers.
[0062] In order to further define the invention, the following
terms and definitions are provided herein.
Definitions
[0063] The term "catalyst system" refers to any system comprising a
catalyst such as a Platinum Group Metal (PGM) catalyst. In some
embodiments, the catalyst system comprises a substrate, a washcoat,
and optionally an overcoat. Select examples of catalyst systems are
depicted in FIGS. 1-5.
[0064] The term "catalytic converter system" refers to a system
comprising one or more catalyst systems. For example, a catalytic
converter system may comprise a close-coupled catalyst system, an
underfloor catalyst, or both.
[0065] The term "close-coupled catalyst" or "CC catalyst" refers
to, for example, a catalytic converter which is placed close to the
engine so as to be exposed to the heat generated by operation of
the engine. Such CC catalysts may be TWC catalysts.
[0066] The term "Ce-containing mixed metal oxide" refers to
materials based on a fluorite structure and containing Ce, Zr and,
typically, several lanthanide metals. Typical examples are
expressed in terms of the relative quantity of Ce and Zr (e.g.,
Ce-rich or Zr-rich). Lanthanides are present as dopants, typically
at 1-10%. Commonly used lanthanides include Pr, Nd, La, Sm, Gd and
Y.
[0067] The term "cold start" refers to the beginning of the
operation of a vehicle after it has been inoperative for a
significant period of time, such that the engine (including the
working components of the exhaust system--e.g., sensors, catalytic
converter(s), etc.) are all at ambient temperature.
[0068] The term "conversion efficiency" refers to the percentage of
emissions passing through the catalyst that are converted to their
target compounds.
[0069] The term "coupled with" refers to a relationship (e.g.,
functional or structural) between components of a catalyst system
(e.g., the relationship between the washcoat and the substrate
and/or overcoat, or the relationship between the overcoat and the
washcoat). In some embodiments, components which are coupled to
each other are in direct contact with each other (e.g., the
washcoat may be in direct contact with and, thus, coupled with the
substrate). In other cases, components which are coupled to each
other are coupled via additional component(s) (e.g., an overcoat is
coupled to the substrate via the washcoat).
[0070] The term "high-surface area alumina" refers to aluminum
oxides that have a high specific surface area--i.e., a high surface
area per unit weight. High surface area aluminas typically have
crystal structures designated as gamma, delta or theta.
[0071] The term "high-temperature conditions" refers to engine
conditions wherein hot exhaust gas passes through a catalyst. Such
exhaust gas is typically in excess of 800.degree. C., and in
extreme circumstances, in excess of 1000.degree. C.
[0072] The term "Lanthanide group of elements" refers to the
elements La, Pr, Sm, Nd, Pm, Gd, Eu, Tb, Dy, Ho, Er, Tm, Yb and
Lu.
[0073] The term "Ln-doped Zirconia" refers to an oxide comprising
zirconium and an amount of dopant from the lanthanide group of
elements, where Ln denotes any of the lanthanide group.
[0074] The term "light-off temperature" refers to the temperature
at which a catalyst is able to convert 50% of the emissions passing
through the catalyst (e.g., nitrogen oxides, carbon monoxide and
unburnt hydrocarbons) to their target compounds (e.g., nitrogen and
oxygen, carbon dioxide, and carbon dioxide and water,
respectively).
[0075] The term "multiphase catalyst" or "MPC" refers to a catalyst
represented by the general formula
Ce.sub.yLn.sub.1-xA.sub.x+sMO.sub.z. Such catalysts are described
in, e.g., U.S. Pat. No. 7,641,875, which is hereby incorporated by
reference in its entirety.
[0076] The term "mixed metal oxide" refers to an oxide, wherein the
cation positions in the oxide's crystal structure can be occupied
by a variety of cations. Such cations may be selected from one or a
variety of lanthanides.
[0077] The term "overcoat" refers to a coating comprising one or
more oxide solids that are coupled with a substrate and a washcoat.
The oxide solids in the overcoat may be, for example, support
oxides, one or more catalyst oxides, or a mixture of support oxides
and catalyst oxides.
[0078] The term "oxygen storage capacity" or "OSC" refers to the
ability of the oxygen storage material component of a TWC catalyst
to store oxygen. TWC catalysts with high oxygen storage capacities
are able to supply oxygen to rich exhaust and take up oxygen from
lean exhaust, thus buffering a catalyst system against the
fluctuating supply of oxygen by maintaining a steady air/fuel
ratio. This process increases catalyst efficiency. Oxygen storage
capacity is typically measured in terms of "delay in time"--i.e.,
the amount of time the oxygen storage material is able to absorb
and/or release oxygen, thus buffering the air/fuel ratio. The
air/fuel ratio is preferably buffered at the stoichiometric
ratio.
[0079] The term "oxygen storage material" or "OSM" refers to a
composition which supplies oxygen to rich exhaust and takes up
oxygen from lean exhaust, thus buffering a catalyst system against
the fluctuating supply of oxygen. Oxygen storage materials increase
catalyst efficiency. Oxygen storage materials may be present in the
washcoat and/or the overcoat of a catalyst composition.
[0080] The term "platinum group metal" or "PGM" refers to one of
the following six elements: ruthenium (Ru), rhodium (Rh), palladium
(Pd), osmium (Os), iridium (Ir), and platinum (Pt).
[0081] The term "poisoning" or "catalyst poisoning" refers to the
inactivation of a catalyst by virtue of its exposure to lead or
phosphorus in, for example, engine exhaust.
[0082] The term "rare-earth metal" refers to any lanthanide element
of the periodic table of the chemical elements.
[0083] The term "solid solution" refers to the doping of a metal
either onto the crystallographic site of a host material, or in
between crystallographic sites of a host material. Such solid
solutions are composed of a single homogenous phase. The solid
solution has the same crystallographic type or structure as the
un-doped host material. Typically the lattice parameters of the
solid solution increase or decrease with increasing dopant amount.
Whether or not an increase or decrease in lattice parameters occurs
depends on whether the doping cation is smaller or larger than the
host cations (in addition to other specific chemical and
crystallographic factors).
[0084] The term "solid solution limit" refers to the maximum amount
of dopant that can exist on the host sites in a solid solution.
Above this limit, any increase in the amount of dopant produces a
two-phase material: 1) a phase comprising the solid solution (with
the maximum dopant level); and 2) a phase comprising the excess
dopant.
[0085] The term "stoichiometric point" or "stoichiometric ratio"
refers to a particular air-fuel ratio (i.e., the ratio of air to
fuel present in an engine during combustion). An engine operates at
the stoichiometric point when exactly enough air is present in the
fuel mixture to burn all of the fuel present.
[0086] The term "stabilized alumina" refers to alumina wherein
modifiers are added to retard undesired phase transitions of the
alumina from, for example, the gamma phase to the alpha phase, when
the alumina is exposed to elevated temperatures. Such modifiers aid
in stabilizing the surface area of the alumina. Alumina is exposed
to high temperatures during formation of the catalyst system and
during operation of the catalyst system (e.g., when it is exposed
to exhaust gas). The modifiers or thermal stabilizers may include,
for example, one or more modifiers or stabilizers selected from,
but not limited to, rare earth oxides, silicon oxides, oxides of
Group IVB metals (e.g., zirconium, hafnium, or titanium) and
alkaline earth oxides. For example, lanthanide nitrate and/or
strontium nitrate may be added to washcoats and/or overcoats (in,
e.g., support oxides) as a modifier for the alumina. The lanthanide
nitrate solution may contain a single lanthanide nitrate (e.g.,
lanthanum nitrate), or the solution may contain a mixture of
lanthanide nitrates. Heating or calcining the lanthanide nitrate
and/or strontium nitrate forms lanthanide oxide (Ln.sub.2O.sub.3)
and/or strontium oxide.
[0087] The term "substrate" refers to any material known in the art
for supporting a catalyst. Substrates can be of any shape or
configuration that yields a sufficient surface area for the deposit
of the washcoat and/or overcoat. Examples of suitable
configurations for substrates include, but are not limited to,
honeycomb, pellet, and bead configurations. Substrates can be made
of a variety of materials including, but not limited to alumina,
cordierite, ceramic and metal.
[0088] The term "support oxide" refers to porous solid oxides which
are used to provide a high surface area which aids in oxygen
distribution and exposure of catalysts to reactants such as
NO.sub.x, CO, and hydrocarbons. Support oxides are typically mixed
metal oxides. Support oxides typically have a large surface area.
For example, a support oxide may have a BET (Brunauer, Emmett and
Teller) surface area of 60 m.sup.2/g or more and, often, about 200
m.sup.2/g or more. In general, support oxides should remain stable
in the presence of exhaust gas temperatures which can reach up to
800-1100.degree. C. Suitable compounds for use as support oxides
include, but are not limited to, gamma-alumina, ceria-based
powders, or any mixture of titania, silica, alumina (transition and
alpha-phase), ceria, zirconia,
Ce.sub.1-.alpha.Zr.sub..alpha.O.sub.2, and any possible doped ceria
formulations. A transition phase is a meta-stable phase of alumina
(beta, gamma, theta, delta) that transforms to the stable
alpha-alumina with sufficient time and temperature.
[0089] The term "three-way conversion catalyst" or "'MC catalyst"
refers to a catalyst that simultaneously: a) reduces nitrogen
oxides to nitrogen and oxygen; b) oxidizes carbon monoxide to
carbon dioxide; and c) oxidizes unburnt hydrocarbons to carbon
dioxide and water. Typically, TWC catalysts require the use of
precious metals such as platinum group metals.
[0090] The term "transition metal" refers to any element of the d
block of the periodic table of the chemical elements.
[0091] The term "washcoat" refers to a coating comprising one or
more oxide solids that is coupled to a substrate or solid support
structure. The oxide solids in the washcoat may be, for example,
support oxides, one or more catalyst oxides, or a mixture of
support oxides and catalyst oxides.
Catalyst Systems
[0092] Catalyst systems in, for example, catalytic converters may
be used in conjunction with an internal combustion engine. Thus, in
some embodiments, the catalyst of the catalyst system is a TWC
catalyst. In light of the expense associated with Rh-containing
catalyst systems, there remains a need for catalyst systems with
reduced Rh-loadings that retain the ability to efficiently purify
engine exhaust. Thus, in one aspect, the present invention provides
catalyst system components which contain little to no Rh and, when
incorporated into catalyst systems, are able to participate in
efficient TWC of compounds in engine exhaust.
[0093] The catalyst systems (including TWC catalyst systems) of the
present invention may have a variety of architectures. TWC catalyst
systems typically comprise (1) a substrate, (2) a washcoat
supported by the substrate, and (3) an optional overcoat supported
by the washcoat (see FIGS. 1-5). For example, the TWC catalyst
systems of the present invention may comprise (1) a substrate, and
(2) a washcoat containing at least one metal catalyst, wherein the
washcoat is supported by the substrate (see FIG. 1). The catalyst
systems of the present invention may also comprise (1) a substrate,
(2) a washcoat containing at least one metal catalyst, wherein the
washcoat is supported by the substrate, and (3) an overcoat
containing at least one metal catalyst, wherein the overcoat is
supported by the washcoat (see, FIG. 2). The catalyst systems of
the present invention may also comprise (1) a substrate, (2) a
washcoat containing at least one metal catalyst, wherein the
washcoat is supported by the substrate, and (3) an overcoat which
is relatively free of metal catalyst, preferably at least 95%, 99%,
or at least 99.99% free of metal catalyst, or completely free of
metal catalyst (see FIG. 3). Further, the catalyst systems of the
present invention may comprise (1) a substrate, (2) a washcoat
which is relatively free of metal catalyst, preferably at least
95%, 99%, or at least 99.99% free of catalyst, or completely free
of metal catalyst, and (3) an overcoat containing at least one
metal catalyst, wherein the overcoat is supported by the washcoat
(see, FIG. 4).
[0094] Catalyst systems are typically present in two locations in
automobile engines. For example, an automobile may contain two
catalytic converters: 1) a close-coupled catalyst ("CC catalyst")
placed near the engine; and 2) a larger catalyst placed, for
example, under the floor of the vehicle where there is more room
("underfloor catalyst" of "UF catalyst"). CC catalysts are placed
near the engine so they are exposed to the heat generated by
operation of the engine. This heat allows the CC catalyst to more
quickly reach its light-off temperature and, thus, more quickly
reach its maximum efficiency. CC catalysts, however, suffer for at
least two major drawbacks. First, their exposure to high
temperatures leads to thermal degradation of the catalyst system.
Second, their close proximity to the engine exposes them to a
higher amount of phosphorus and sulfur which acts to poison the
catalyst. The improved catalyst system components of the present
invention address these issues.
Improved Catalyst Systems
[0095] One aspect of the present invention is the provision of
catalyst system components which allow for efficient TWC conversion
with little or no Rh-based catalysts. Such components may be used
in the washcoat and/or overcoats of catalyst systems. Specifically,
the present invention provides oxygen storage materials (OSMs) for
using in washcoats and/or overcoats which contain reduced amounts
of Rh-based catalysts. In some embodiments, the OSMs contain no
Rh-based catalysts.
Pd-Based Oxygen Storage Materials (Pd-OSMs)
[0096] The OSMs of the present invention have several advantages
over OSMs traditionally used in catalyst systems such as catalytic
converters. As discussed herein, these advantages include, for
example, improved oxygen storage capacity ("OSC"), light-off
temperatures, and catalyst efficiency. The incorporation of the
OSMs of the present invention into catalyst systems has a
beneficial impact on the overall performance of such systems.
[0097] The OSMs of the present invention contain a catalyst, such
as a Pd, wherein the catalyst is present as a solid solution ("SS")
within the OSM (i.e., a SS Pd-OSM). For example, a SS Pd-OSM of the
present invention would comprise Pd present as a solid solution
within a Ce-containing mixed metal oxide. Without being bound by a
particular theory, it is believed that when Pd is present in a SS
with the OSM, it is evenly dispersed throughout the OSM and the
surface of the OSM (see Examples 7-9 and FIGS. 17-18). The even
dispersion of Pd on the surface of the OSM allows for improved
access of the Pd to both oxygen and substrates in the exhaust. In
addition, the Pd dispersion allows for more facile diffusion of
oxygen from within the OSM to the surface of the OSM.
[0098] When the Pd is present as a SS, the Pd cations are doped
onto the OSMs to yield the SS Pd-OSMs of the present invention.
Without being bound by a particular theory, it is believed that the
doping of the OSM with Pd leads to the observed performance
benefits of the SS Pd-OSMs of the present invention. For example,
as discussed herein, the SS Pd-OSMs of the present invention
display higher OSCs when compared to traditional catalysts and
OSMs. The doping of the OSM with Pd replaces a Ce.sup.4+ ion of the
Ce-containing mixed metal oxide with a Pd.sup.2+ ion. As a result
of this doping, the SS Pd-OSM comprises ions with a lower charge
(i.e., Pd.sup.2+ vs Ce.sup.4+) which, in turn, creates a vacancy
which may be occupied by additional O.sup.2- ions. (see, Example 10
and FIG. 6). Thus, there is a drive to form vacancies in order to
balance the overall charge of the system.
[0099] The increased ability to accommodate O.sup.2- (i.e., to
absorb O.sup.2- into the OSM) results in an increase in raw OSC. In
addition, the vacancies formed by Pd.sup.2+ incorporation (and
Ce.sup.4+ replacement) allow for more facile diffusion of O.sup.2-
from the interior to the surface of the OSM (sometimes referred to
as O.sup.2- "hopping" between layers of the Ce-mixed metal oxide).
Such an improvement is useful as O.sup.2- must be able to freely
move to the surface of the OSM in order to access substrates
present in engine emissions and to buffer the catalyst environment
in case of exposure to a lean or rich air/fuel mixture (see,
Example 10 and FIG. 7).
[0100] The dispersed Pd found in the SS Pd-OSM of the present
invention is significantly different in structure when compared to
bulk form Pd. Bulk form Pd, which is typically formed when
traditional methods are used to generate catalyst systems, is
agglomerated as large particles on the surface of the OSM.
Agglomerated Pd is not considered to be in a SS. Instead, the
agglomerated Pd is largely present as clumps of Pd (as PdO) on the
surface of the OSM--i.e., it is in a different phase from the OSM.
This form of Pd is less capable of interacting with oxygen and
substrates in the exhaust. In addition, Pd present as PdO on the
surface of the OSM does not positively contribute to OSC.
Specifically, PdO does not allow for the replacement of Ce.sup.4+
with Pd.sup.2+ throughout the OSM.
[0101] Pd in bulk form and present on the surface of the OSM is
more thermodynamically stable when compared to Pd dispersed as a SS
throughout the OSM. Yet, the SS Pd-OSMs of the present invention
are suitable for use in catalyst systems which are routinely
exposed to high temperatures. It is believed that the metastability
of the Pd dispersed as a SS throughout the OSM allows for the
maintenance of Pd in SS form. Thus, even though the bulk form Pd is
the more thermodynamically stable form, the significant energy
required to drive the Pd from its SS form to the bulk form Pd
allows catalyst to remain in SS form (see FIG. 8).
[0102] The amount of Pd present in the SS Pd-OSMs affects the form
of the Pd. For example, attempts to dope the OSM with high amounts
of Pd are typically met with lackluster rates of Pd incorporation
into the OSM as a SS. The use of high amounts of Pd in the doping
process leads to the undesirable formation of PdO particles on the
surface of the OSM (see Examples 7-9 and FIGS. 16-20).
[0103] Thus, in some embodiments, the OSM is doped with
approximately 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%,
5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10% Pd. In some
embodiments, the OSM is doped with approximately 0.5-10%, 0.5-5%,
0.5-4.5%, 0.5-4%, 0.5-3.5%, 0.5-3%, 0.5-2.5%, 0.5-2%, 1-3% or 1-2%
Pd. In some embodiments, the OSM is doped with approximately 2%,
2.21% or 4.08% Pd. In particular embodiments, the OSM is doped with
2%, 2.21% or 4.08% Pd.
[0104] In other embodiments, the OSM is doped with up to
approximately 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%,
5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10% Pd. In some
embodiments, the OSM is doped with up to approximately 0.5-10%,
0.5-5%, 0.5-4.5%, 0.5-4%, 0.5-3.5%, 0.5-3%, 0.5-2.5%, 0.5-2%, 1-3%
or 1-2% Pd. In some embodiments, the OSM is doped with up to
approximately 2%, 2.21% or 4.08% Pd. In particular embodiments, the
OSM is doped with up to 2%, 2.21% or 4.08% Pd.
Improved Performance of SS Pd-OSMs
[0105] It has been found that SS Pd-OSMs are able to efficiently
catalyze the conversion of compounds present in, for example,
engine exhaust without the need for supporting a catalyst on a
support oxide. While the SS Pd-OSMs of the present invention are
able to efficiently participate in the general TWC of engine
exhaust, they are particularly efficient in catalyzing the
conversion of CO to CO.sub.2. The oxidation of CO is particularly
exothermic and, thus, beneficial to the SS Pd-OSMs. Thus, the SS
Pd-OSMs of the present invention are able to more quickly reach
their light-off temperature in part due to the heat generated from
the CO oxidation reaction. In addition, the SS Pd-OSMs of the
present invention are able to reach a higher operating
temperature--again stemming from the exothermic CO oxidation (see
Example 5 and FIG. 15).
[0106] This self-heating process enables the use of the SS Pd-OSMs
in catalysts placed further away from the engine--i.e., there is
less need to place SS Pd-OSMs in catalyst systems that are near
engines. There are benefits to such systems, including the reduced
thermal degradation of the precious metal catalysts and the reduced
amount of catalyst poisoning. These benefits are observed in the
context of the Federal Test Procedure drive cycle (i.e., standard
operating temperature). In addition, these benefits are observed in
the context of CC-catalyst and underfloor catalysts (see Example 4
and Table 4).
[0107] Interestingly, additional benefits of SS Pd-OSMs allow them
to be used even in CC catalysts. Specifically, it has been shown
that the SS Pd-OSMs reduce the aging of the Pd catalyst present,
even if it is present in a high-heat environment and even without
the presence of BaCO.sub.3 or La--Al.sub.2O.sub.3. Moreover, the SS
Pd-OSMs of the present invention also reduce the poisoning of the
Pd catalyst. This may be due to the lack of nano-scale Pd particles
onto which poisons normally bond or associate.
[0108] As discussed above, SS Pd-OSMs exhibit improved OSCs
compared to standard catalyst systems (e.g., MPCs). OSC is a
measure of an OSM's ability to supply oxygen to rich exhaust and
take up oxygen from lean exhaust, thus buffering a catalyst system
against the fluctuating supply of oxygen by maintaining a steady
air/fuel ratio. In some embodiments, the SS Pd-OSMs of the present
invention are able to buffer the air/fuel ratio at the
stoichiometric point.
[0109] The OSC of an OSM is typically measured by exposing the OSM
to either lean or rich air/fuel mixtures. In such environments, the
OSM must either absorb O.sub.2 from the exhaust stream (e.g., in
lean air/fuel mixture environments) or release O.sub.2 (e.g., in
rich air/fuel mixture environments) in order to maintain efficient
catalysis of exhaust compounds. The amount of time for which an OSM
can buffer the lean/rich air/fuel mixture is one way to quantify
the OSC of an OSM. This time is usually referred to as the "delay
time"--i.e., the amount of time that it takes for a perturbation in
the air/fuel mixture to manifest itself as a change in O.sub.2
levels within the catalyst environment. The delay time can also be
measured by the amount of time that it takes for a perturbation in
the air/fuel mixture to manifest itself as a change in CO levels
within the catalyst environment.
[0110] In some embodiments of the present invention, the SS Pd-OSM,
such as SS Pd-IWCP OSM, exhibits a CO delay time of approximately
2-25, 2-20, 5-20, 5-15, 7-15, 10-15, or 12-15 seconds when exposed
to a rich air/fuel mixture. In some embodiments, the SS Pd-OSM
exhibits a CO delay time of approximately 2, 3, 4, 5, 6, 7, 8, 9,
10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 or 25,
or more, seconds when exposed to a rich air/fuel mixture. In some
embodiments, the SS Pd-OSM exhibits a CO delay time of up to
approximately 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,
17, 18, 19, 20, 21, 22, 23, 24 or 25, or more, seconds when exposed
to a rich air/fuel mixture. In some embodiments, the SS Pd-OSM
exhibits a CO delay time of at least approximately 2, 3, 4, 5, 6,
7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24
or 25, or more, seconds when exposed to a rich air/fuel mixture. In
a particular embodiment, the OSM exhibits a delay time of
approximately 14 seconds when exposed to a rich air/fuel mixture.
In another particular embodiment, the OSM exhibits a delay time of
14.3 seconds when exposed to a rich air/fuel mixture.
[0111] In other embodiments, the OSM exhibits an O.sub.2 delay time
of approximately 2-33, 2-30, 2-28, 5-28, 5-25, 5-20, 8-20, 8-18,
8-16, 10-16, 12-16, or 14-16 seconds when exposed to a lean
air/fuel mixture. In some embodiments, the OSM exhibits an O.sub.2
delay time of approximately 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,
14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30,
31, 32 or 33, or more, seconds when exposed to a lean air/fuel
mixture. In other embodiments, the OSM exhibits an O.sub.2 delay
time of up to approximately 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,
14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30,
31, 32 or 33, or more, seconds when exposed to a lean air/fuel
mixture. In other embodiments, the OSM exhibits a delay time of at
least approximately 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32
or 33, or more, seconds when exposed to a lean air/fuel mixture. In
a particular embodiment, the OSM exhibits a delay time of
approximately 23 seconds when exposed to a lean air/fuel mixture.
In another particular embodiment, the OSM exhibits a delay time of
22.7 seconds when exposed to a lean air/fuel mixture.
[0112] The SS Pd-OSMs of the present invention also exhibit
increased catalytic efficiency and are particularly useful in high
engine speed environments Improved OSCs are especially important in
these environments because of the very high temperatures and
exhaust stream space velocities present (see Example 3 and FIGS.
13-14). These high temperature and high speed conditions make it
difficult to maintain conversion efficiencies of NO.sub.x, CO and
hydrocarbons, resulting in increased tailpipe emissions. Without
being bound by a particular theory, it may be that the high speed
conditions produce a high velocity exhaust gas which reduces the
amount of time the exhaust interacts with the catalyst sites.
[0113] As engine speeds fluctuate during normal use, the air/fuel
mixture may also fluctuate. Thus, the SS Pd-OSMs of the present
invention are better able to buffer the air/fuel mixture present in
exhaust from engines operating at varying speeds (see Example 3,
and FIGS. 13-14).
Catalyst Systems Comprising SS Pd-OSMs
Overview
[0114] The catalyst systems (including TWC catalyst systems) of the
present invention may have a variety of architectures. For example,
a catalytic converter system present in an automobile may contain
both a CC catalyst and an UF catalyst, wherein the CC catalyst is
placed closer to the engine in comparison to the UF catalyst.
[0115] Both CC and/or UF catalysts typically comprise (1) a
substrate, (2) a washcoat supported by the substrate, and (3) an
optional overcoat supported by the washcoat. In particular
embodiments, the CC and/or UF catalyst comprises (1) a substrate,
(2) a washcoat supported by the substrate, and (3) an overcoat
supported by the washcoat. In some embodiments of the present
invention, the catalyst systems comprise CC and UF catalysts
comprising a SS Pd-OSM. The SS Pd-OSM may be present in either the
washcoat, the overcoat, or both of either the CC catalyst, UF
catalyst, or both. In particular embodiments, the catalyst systems
comprise (1) a substrate, (2) a washcoat comprising a multi-phase
catalyst (MPC), wherein the washcoat is supported by the substrate,
and (3) an overcoat comprising a SS Pd-OSM, wherein the overcoat is
supported by the washcoat.
[0116] In particular embodiments wherein the catalytic converter
system comprises both a CC and UF catalyst, the CC catalyst
comprises (1) a substrate, (2) a washcoat comprising a MPC, wherein
the washcoat is supported by the substrate, and (3) an overcoat
comprising a SS Pd-OSM, wherein the overcoat is supported by the
washcoat. The CC catalyst overcoats and washcoats are substantially
free, and preferably completely free, of Rh. In some embodiments,
the CC catalyst overcoats and washcoats contain Pd as the metal
catalyst. The CC catalyst washcoats may comprise perovskite-type
compounds which are present as a phase of the MPC and which
function as OSMs. In some embodiments, the metal catalyst (such as
Pd) present in the CC catalyst washcoat is supported only by the
perovskite-type compound. The CC catalyst washcoats and overcoats
may contain additional components/additives as described
herein.
[0117] In some embodiments wherein the catalytic converter system
comprises both a CC and UF catalyst, the UF catalyst has the same
composition as the CC catalyst describe above.
[0118] In particular embodiments wherein the catalytic converter
system comprises both a CC and UF catalyst, the UF catalyst
comprises (1) a substrate, (2) a washcoat comprising a MPC, wherein
the washcoat is supported by the substrate, and (3) an overcoat
comprising a MPC, wherein the overcoat is supported by the
washcoat. In such embodiments, the UF catalyst may contain Pd
and/or Rh as metal catalysts. In some embodiments, the UF washcoat
may contain Pd as a metal catalyst while the UF overcoat contains
Rh as a metal catalyst. As discussed in the context of the CC
catalysts, the UF catalyst washcoats and overcoats may contain
additional components/additives as described herein. In addition,
the UF catalyst washcoats and overcoats may comprise
perovskite-type compounds which are present as a phase of the MPC
and which function as OSMs. In some embodiments, the metal catalyst
present in the UF catalyst washcoats and overcoats are supported
only by the perovskite-type compound.
Substrates
[0119] A variety of materials are appropriate as substrates for the
present invention. For example, the substrate may be a refractive
material, a ceramic substrate, a honeycomb structure, a metallic
substrate, a ceramic foam, a metallic foam, a reticulated foam, or
suitable combinations, where the substrate has a plurality of
channels and at least the required porosity. As is known in the
art, the number of channels present may vary depending upon the
substrate used. It is preferred that the substrate offer a
three-dimensional support structure.
[0120] The substrate may be in the form of beads or pellets. In
such embodiments, the beads or pellets may be formed from, for
example, alumina, silica alumina, silica, titania, mixtures
thereof, or any suitable material. In a particular embodiment, the
substrate may be a honeycomb substrate, for example a ceramic
honeycomb substrate or a metal honeycomb substrate. The ceramic
honeycomb substrate may be formed from, for example, sillimanite,
zirconia, petalite, spodumene (lithium aluminum silicate),
magnesium silicates, mullite, alumina, cordierite, other
alumino-silicate materials, silicon carbide, aluminum nitride, or
combinations thereof. Other ceramic substrates would be apparent to
one of ordinary skill in the art.
[0121] In embodiments wherein the substrate is a metal honeycomb
substrate, the metal may be, for example, a heat-resistant base
metal alloy, particularly an alloy in which iron is a substantial
or major component. In addition, metal substrate surface may be
oxidized at elevated temperatures (e.g., above about 1000.degree.
C.) to improve the corrosion resistance of the alloy by forming an
oxide layer on the surface of the alloy. This oxide layer on the
surface of the alloy may also enhance the adherence of a washcoat
to the surface of the monolith substrate.
[0122] In one embodiment, the substrate may be a monolithic carrier
having a plurality of fine, parallel flow passages extending
through the monolith. Such passages may be of any suitable
cross-sectional shape and/or size. For example, such passages may
be trapezoidal, rectangular, square, sinusoidal, hexagonal, oval,
or circular, although other shapes are also suitable. The monolith
may contain from about 9 to about 1200 or more gas inlet openings
or passages per square inch of cross section, although fewer
passages may be used.
Washcoats
[0123] The washcoats of the catalyst systems of the present
invention typically comprise, inter alia, a metal catalyst, an OSM,
a support oxide, and additives which aid in retarding metal
catalyst poisoning.
[0124] Such washcoats may comprise multiphase catalysts (MPCs) and
may generally be produced using standard techniques known in the
art (see, for example, U.S. Pat. No. 7,641,875). See also Example
1. MPCs typically comprise, inter alia, a metal catalyst, an OSM,
and a support oxide, and are represented by the general formula
Ce.sub.yLn.sub.1-xA.sub.x+sMO.sub.z, wherein: [0125] A is an
element selected from the group consisting of Mg, Ca, Sr, Ba, Li,
Na, K, Cs, Rb, La and any combination thereof, preferably La, Ca or
Ba and more preferably Ba; [0126] Ln is a mixture of elements
originally in the form of single-phase mixed lanthanides collected
from natural ores, a single lanthanide, or a mixture of artificial
lanthanides, preferable La; [0127] M is an element selected from
the group consisting of Fe, Mn, Cr, Ni, Co, Cu, V, Zr, Pt, Pd, Rh,
Ru, Ag, Au, Al, Ga, Mo, W, Ti, and any combination thereof,
preferably Pd, and preferably not Rh; [0128] x is a number defined
by 0.ltoreq.x<1.0; [0129] y is a number defined by
0.ltoreq.y<10; [0130] s is a number defined by 0.ltoreq.s<10;
and [0131] z is a number defined by z>0, [0132] where s=0 only
when y>0 and y=0 only when s>0.
[0133] Washcoats present in the catalyst systems of the present
invention may comprise perovskite-type compounds which are present
as a phase of the MPC and which function as OSMs. In some
embodiments, the metal catalyst present in the washcoat is
supported only by the perovskite-type compound. Washcoats which
comprise metal catalysts supported only by the perovskite-type
compound are typically found in CC catalysts.
[0134] It has been observed that the amount (or thickness) of the
washcoat present, wherein the same amount of catalyst is present in
washcoats of varying thicknesses, can affect certain properties of
the catalyst system. For example, the thickness of the washcoat can
affect thermal and phosphorus (poisoning) aging as measured by the
OSC, light-off temperatures ("T90s"), and conversion efficiencies
(i.e., conversion of nitrogen oxides, carbon monoxide and unburnt
hydrocarbons to their target compounds) after exposure to heat and
poisoning agents such as phosphorus.
[0135] Increasing the total amount of washcoat, while keeping the
amount of catalyst constant, has a beneficial effect on the OSC of
catalyst systems which have been aged by either exposure to heat or
simultaneous exposure to heat and phosphorus (see Examples 15 and
16 and Tables 11-12). Interestingly, while increasing the washcoat
thickness improves the OSC after thermal aging, the OSC effect
appears to taper in systems which have been exposed to simultaneous
thermal and phosphorus aging. For example, as the washcoat
thickness is increased from 150 g/L.fwdarw.180 g/L.fwdarw.210 g/L,
a maximum beneficial effect on OSC is observed at 180 g/L (see
Examples 15 and 16 and Tables 11-12). Without being bound by a
particular theory, the decreased OSC benefit observed at 210 g/L
may be due to the fact that the catalyst (in this case, Pd) is
present at too dilute of a concentration at this large washcoat
volume to effect the OSC.
[0136] In addition, it has been generally found that increasing the
total amount of washcoat present in the catalyst system decreases
(i.e., improves) the light-off temperature of the system, likely
due to the fact that a larger mass of cold material takes longer to
heat up.
[0137] Moreover, increasing the total amount of washcoat has a
beneficial effect on the conversion efficiencies of the catalyst
system after thermal and phosphorus aging (see Examples 15 and 16
and Tables 11-12).
[0138] Thus, in some embodiments, the catalyst system of the
present invention comprises a washcoat, where the washcoat is
present at between about 100 g/L-250 g/L. In some embodiments, the
washcoat is present at between about 120 g/L-210 g/L, 150 g/L-210
g/L, 120 g/L-180 g/L, 120 g/L-150 g/L, or 150 g/L-180 g/L. In some
embodiments, the washcoat is present at about 120 g/L, 150 g/L, 180
g/L, or 210 g/L. In particular embodiments, the washcoat is present
at 120 g/L, 150 g/L, 180 g/L, or 210 g/L.
[0139] In other embodiments, the catalyst system of the present
invention comprises a washcoat, where the washcoat is present at
between up to about 100 g/L-250 g/L. In some embodiments, the
washcoat is present at between up to about 120 g/L-210 g/L, 150
g/L-210 g/L, 120 g/L-180 g/L, 120 g/L-150 g/L, or 150 g/L-180 g/L.
In some embodiments, the washcoat is present at up to about 120
g/L, 150 g/L, 180 g/L, or 210 g/L. In particular embodiments, the
washcoat is present at up to 120 g/L, 150 g/L, 180 g/L, or 210
g/L.
[0140] The washcoats of the catalyst systems of the present
invention may contain additives which aid in retarding the
poisoning of precious metal catalysts by phosphorus and sulfur.
Consumption of engine lubricants results in the generation of
phosphorus and, in turn, the poisoning and deactivation of precious
metal catalysts. Thus, additives such as calcium, barium,
lanthanides and/or cerium may be added to the washcoats and/or
overcoats (if present) as a means of retarding the poisoning
process. In some embodiments, the additive is CaCO.sub.3,
La.sub.2O.sub.3 or BaCO.sub.3. In a particular embodiment, the
additive is BaCO.sub.3.
[0141] Without being bound by a particular theory, the addition of
barium provides a barium source (BaCO.sub.3) which is able to react
with exhaust phosphorus to form a stable compound (i.e.,
Ba.sub.3(PO.sub.4).sub.2). Because the reaction of BaCO.sub.3 with
exhaust phosphorus is thermodynamically favored and the
Ba.sub.3(PO.sub.4).sub.2 product is thermodynamically stable, the
barium acts to efficiently trap passing exhaust phosphorus in a
form which does not poison the metal catalyst (see Examples 12 and
13 and FIG. 9). It is noted that, upon exposure to exhaust
containing, for example phosphorus, CaCO.sub.3, La.sub.2O.sub.3 and
BaCO.sub.3 are converted to Ca.sub.3(PO.sub.4).sub.2, LaPO.sub.4
and Ba.sub.3(PO.sub.4).sub.2, respectively.
[0142] In some embodiments, the additive, such as La.sub.2O.sub.3
or BaCO.sub.3, is impregnated into the washcoat at a concentration
of 6M.
Overcoats
[0143] The overcoats of the catalyst systems of the present
invention may comprise, inter alia, a metal catalyst, an OSM, a
support oxide, and an additive which aids in retarding metal
catalyst poisoning.
[0144] The overcoats of the present invention may comprise MPCs as
discussed in the context of the washcoats and, thus, may be
generated using the techniques and methods described in, for
example, U.S. Pat. No. 7,641,875). See also Example 1.
[0145] The overcoats of the present invention may also comprise SS
Pd-OSMs instead of MPCs, as discussed herein. In such embodiments,
the overcoat may be generated using the IWCP. (see Example 2).
Thus, in some embodiments, the overcoats of the present invention
comprise, inter alia, a catalyst, a SS Pd-OSM, and an additive
which aids in retarding catalyst poisoning. In other embodiments,
the overcoat may further contain an amount of a support oxide which
serves to improve the stability of the overcoat, as discussed
below. In some embodiments, the SS Pd-OSM is present in the
overcoat of the CC catalyst, but not the washcoat of the CC
catalyst nor in the washcoat or overcoat of the UF catalyst.
[0146] As discussed in the context of the washcoats above, the
overcoats of the catalyst systems may also contain additives which
aid in retarding the poisoning of precious metal catalysts by
phosphorus and sulfur. For example, calcium, barium, lanthanides
and/or cerium may be added to the overcoats as a means of retarding
the poisoning process. In some embodiments, the additive is
CaCO.sub.3, La.sub.2O.sub.3 or BaCO.sub.3. In a particular
embodiment, the additive is BaCO.sub.3.
[0147] It has been found that the addition of BaCO.sub.3 to the
overcoat improves certain properties of the catalyst system,
presumably due to the reduction in catalyst poisoning. For example,
the addition of BaCO.sub.3 yields overcoats whose conversion
efficiencies (i.e., conversion of nitrogen oxides, carbon monoxide
and unburnt hydrocarbons to their target compounds) resist aging.
The addition of BaCO.sub.3 to the overcoat significantly improves
the nitrogen oxide and carbon monoxide performance (conversion
efficiency) of catalysts after phosphorus aging when compared to
overcoats which do not contain BaCO.sub.3. In addition, overcoat
containing BaCO.sub.3 maintain a high level of total hydrocarbon
conversion (see Example 14, Table 9). Interestingly, the addition
of 20 grams of BaCO.sub.3 appears to yield the most marked
beneficial effects on conversion efficiencies.
[0148] Accordingly, in some embodiments, the overcoat comprises
0-50 g/L of BaCO.sub.3. In other embodiments, the overcoat
comprises about 0-10 g/L, 0-20 g/L, 0-30 g/L, 10-20 g/L, 10-30 g/L,
or 15-25 g/L of BaCO.sub.3. In other embodiments, the overcoat
comprises about 25-35 g/L, 20-40 g/L, 55-65 g/L, or 50-60 g/L of
BaCO.sub.3. In yet other embodiments, the overcoat comprises about
10 g/L, 20 g/L, 30 g/L, or 60 g/L of BaCO.sub.3. In still other
embodiments, the overcoat comprises about 19-21 g/L, 18-22 g/L,
17-23 g/L, 16-24 g/L, 15-25 g/L, 29-31 g/L, 28-32 g/L, 27-33 g/L,
26-34 g/L, or 25-35 g/L of BaCO.sub.3. In yet other embodiments,
the overcoat comprises about 20 g/L or about 30 g/L of BaCO.sub.3.
In particular embodiments, the overcoat comprises 20 g/L or 30 g/L
of BaCO.sub.3.
[0149] The overcoat may also comprise up to about 0-50 g/L of
BaCO.sub.3. In other embodiments, the overcoat comprises up to
about 0-10 g/L, 0-20 g/L, 0-30 g/L, 10-20 g/L, 10-30 g/L, or 15-25
g/L of BaCO.sub.3. In other embodiments, the overcoat comprises up
to about 25-35 g/L, 20-40 g/L, 55-65 g/L, or 50-60 g/L of
BaCO.sub.3. In yet other embodiments, the overcoat comprises up to
about 10 g/L, 20 g/L, 30 g/L, or 60 g/L of BaCO.sub.3. In still
other embodiments, the overcoat comprises up to about 19-21 g/L,
18-22 g/L, 17-23 g/L, 16-24 g/L, 15-25 g/L, 29-31 g/L, 28-32 g/L,
27-33 g/L, 26-34 g/L, or 25-35 g/L of BaCO.sub.3. In yet other
embodiments, the overcoat comprises up to about 20 g/L or about 30
g/L of BaCO.sub.3. In particular embodiments, the overcoat
comprises up to 20 g/L or 30 g/L of BaCO.sub.3.
[0150] Although overcoats comprising SS Pd-OSMs (e.g., overcoats
present in a CC catalyst) effectively and efficiently purify engine
exhaust without the need for a support oxide, the addition of an
amount of support oxide, such as La--Al.sub.2O.sub.3, to the
overcoat containing the SS Pd-OSM improves certain properties of
the catalyst system. For example, addition of La--Al.sub.2O.sub.3
improves the light off temperature (see Example 14, Table 10).
[0151] Further, the addition of an amount of support oxide, such as
La--Al.sub.2O.sub.3, has been shown to minimize sintering of the
overcoat during the aging process (see, FIG. 10). Sintering is a
solid state mechanism where overcoat (or washcoat) particles
contact and grow through solid-state diffusion. Without being bound
by a particular theory, it is believed that the addition of
La--Al.sub.2O.sub.3 disrupts the single, continuous OSM surface.
This leads to the interspersing of La--Al.sub.2O.sub.3 throughout
the overcoat and, in turn, leads to a decrease in aging-related
sintering by reducing contact between particles of the overcoat. In
addition, it is believed that the dispersion of La--Al.sub.2O.sub.3
throughout the overcoat leads to the formation of relatively open
La--Al.sub.2O.sub.3 pores (see FIG. 10). These pores help to
counteract the physical blocking of the overcoat by exhaust
particulates and, thus, aid to reduce backpressure and increase the
flow of exhaust through the catalyst system.
[0152] It has been observed that the addition of up to 40% (by
weight) of La--Al.sub.2O.sub.3 to the overcoat improves the OSC of
the catalyst system (see Example 11 and FIG. 24). This is likely
due to the improvement in sintering resistance of the OSM.
[0153] In some embodiments, the La--Al.sub.2O.sub.3 present in a SS
Pd-OSM overcoat constitutes about 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%,
9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%,
22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%,
35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%,
48%, 49%, or 50% of the overcoat by weight. In some embodiments,
the La--Al.sub.2O.sub.3 constitutes about 0-50% of the SS Pd-OSM
overcoat by weight. In other embodiments, the La--Al.sub.2O.sub.3
constitutes about 0-10%, 0-20%, 0-30%, or 0-40% of the SS Pd-OSM
overcoat by weight. In other embodiments, the La--Al.sub.2O.sub.3
constitutes about 5-15%, 35-45%, or 30-50% of the SS Pd-OSM
overcoat by weight. In yet other embodiments, the
La--Al.sub.2O.sub.3 constitutes about 9-11%, 8-12%, 7-13%, 6-14%,
5-15%, 39-41%, 38-42%, 37-43%, 36-44%, or 5-15% of the SS Pd-OSM
overcoat by weight. In still other embodiments, the
La--Al.sub.2O.sub.3 constitutes about 10% or 40% of the SS Pd-OSM
overcoat by weight. In particular embodiments, the alumina
constitutes 10% or 40% of the SS Pd-OSM overcoat by weight.
[0154] The La--Al.sub.2O.sub.3 present in the SS Pd-OSM overcoat
may also constitute up to about 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%,
10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%,
23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%,
36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%,
49%, or 50% of the overcoat by weight. In some embodiments, the
La--Al.sub.2O.sub.3 constitutes up to about 0-50% of the SS Pd-OSM
overcoat by weight. In other embodiments, the La--Al.sub.2O.sub.3
constitutes up to about 0-10%, 0-20%, 0-30%, or 0-40% of the SS
Pd-OSM overcoat by weight. In other embodiments, the
La--Al.sub.2O.sub.3 constitutes up to about 5-15%, 35-45%, or
30-50% of the SS Pd-OSM overcoat by weight. In other embodiments,
the La--Al.sub.2O.sub.3 constitutes up to about 10% or 40% of the
SS Pd-OSM overcoat by weight. In particular embodiments, the
alumina constitutes up to 10% or 40% of the SS Pd-OSM overcoat by
weight
[0155] In other embodiments, the SS Pd-OSM overcoat comprises about
0-40 g/L of La--Al.sub.2O.sub.3. In other embodiments, the SS
Pd-OSM overcoat comprises about 0-20 g/L or 5-15 g/L of
La--Al.sub.2O.sub.3. In other embodiments, the SS Pd-OSM overcoat
comprises about 10 g/L of La--Al.sub.2O.sub.3. In particular
embodiments, the SS Pd-OSM overcoat comprises 10 g/L of
La--Al.sub.2O.sub.3.
[0156] In yet other embodiments, the SS Pd-OSM overcoat comprises
up to about 0-40 g/L of La--Al.sub.2O.sub.3. In other embodiments,
the SS Pd-OSM overcoat comprises up to about 0-20 g/L or 5-15 g/L
of La--Al.sub.2O.sub.3. In other embodiments, the SS Pd-OSM
overcoat comprises up to about 10 g/L of La--Al.sub.2O.sub.3. In
particular embodiments, the SS Pd-OSM overcoat comprises up to 10
g/L of La--Al.sub.2O.sub.3.
Metal Catalysts
[0157] The metal catalysts present in the catalyst systems of the
invention are typically present in the washcoat and/or overcoat (if
one is present). Metal catalysts useful for the present invention
include PGM, zirconia, alumina or lanthanide catalysts. In some
embodiments, the catalyst systems comprise one or more metal
catalysts. For example, the washcoat and overcoat may contain the
same metal catalyst or different metal catalysts.
[0158] In some embodiments, the metal catalysts used are PGM
catalysts--i.e., Ru, Rh, Pd, Os, Ir, Pt, or combinations thereof.
In some embodiments, the metal catalysts used are Rh, Pd, Pt, or
combinations thereof. In some embodiments, the metal catalysts used
are Pd, Pt, or combinations thereof. In other embodiments, the
metal catalyst is Pd. In yet other embodiments, the metal catalyst
systems exclude Rh.
[0159] The metal catalyst used in a catalyst system may vary
depending on the location of the metal catalyst. The identity of
the metal catalyst may depend, for example, on whether the metal
catalyst is present in a CC or UF catalyst and may further depend
on whether the metal catalyst is present in the overcoat or
washcoat of the CC or UF catalyst. For example, because Rh is a
particularly expensive precious metal and CC catalysts are exposed
to harsher conditions compared to UF catalysts (e.g., CC catalyst
are exposed to higher heat conditions than UF catalysts) CC
catalysts preferably contain reduced amounts of Rh and more
preferably contain no Rh. In some embodiments, the CC washcoat
contains a reduced amount of Rh, and preferably no Rh. In some
embodiments, the CC overcoat contains a reduced amount of Rh, and
preferably no Rh. In yet other embodiments, both the CC overcoat
and washcoat contain a reduced amount of Rh, and preferably no
Rh.
[0160] However, Rh is more suitable as a catalyst for the UF
catalyst. Thus, in some embodiments, UF catalysts may contain Rh
and/or Pd. In some embodiments, the UF washcoat and overcoat both
contain Rh or both contain Pd. In other embodiments, the UF
overcoat and washcoat contain different catalysts--i.e., one
contains Rh while the other contains Pd. In some embodiments, the
UF overcoat contains Rh while the washcoat contains Pd. In yet
another embodiments, the both the UF overcoat and washcoat contain
Pd.
[0161] The amount of metal catalyst present in the catalyst system
may vary. In some embodiments, the catalyst system comprises a
metal catalyst, such as Pd, at a concentration between about 5-200
g/ft.sup.3, where the metal catalyst may be distributed between the
overcoat (if present) and the washcoat. In embodiments where a
washcoat and overcoat are present, the washcoat and overcoat may
independently comprise a metal catalyst, such as Pd, at a
concentration between about 5-100 g/ft.sup.3. In some embodiments,
the washcoat and overcoat independently comprise a metal catalyst,
such as Pd, at a concentration between about 5-50 g/ft.sup.3, 5-30
g/ft.sup.3, 5-20 g/ft.sup.3, 5-15 g/ft.sup.3, 40-60 g/ft.sup.3,
45-55 g/ft.sup.3, 50-100 g/ft.sup.3, 80-100 g/ft.sup.3, or 90-100
g/ft.sup.3. In some embodiments, the washcoat and overcoat
independently comprise a metal catalyst, such as Pd, at a
concentration of about 5, 10, 15, 20, 50 or 100 g/ft.sup.3. In
particular embodiments, the washcoat and overcoat independently
comprise a metal catalyst, such as Pd, at a concentration of 5, 10,
15, 20, 50 or 100 g/ft.sup.3.
[0162] In some embodiments, the washcoat and overcoat independently
comprise a metal catalyst, such as Pd, at a concentration up to
between about 5-50 g/ft.sup.3, 5-30 g/ft.sup.3, 5-20 g/ft.sup.3,
5-15 g/ft.sup.3, 40-60 g/ft.sup.3, 45-55 g/ft.sup.3, 50-100
g/ft.sup.3, 80-100 g/ft.sup.3, or 90-100 g/ft.sup.3. In some
embodiments, the washcoat and overcoat independently comprise a
metal catalyst, such as Pd, at a concentration of up to about 5,
10, 15, 20, 50 or 100 g/ft.sup.3. In particular embodiments, the
washcoat and overcoat independently comprise a metal catalyst, such
as Pd, at a concentration of up to 5, 10, 15, 20, 50 or 100
g/ft.sup.3.
[0163] In some embodiments, the overcoat comprises a metal
catalyst, such as Pd, at a concentration between about 0-50
g/ft.sup.3, 0-30 g/ft.sup.3, 0-20 g/ft.sup.3, 0-15 g/ft.sup.3, 0-10
g/ft.sup.3, 0-5 g/ft.sup.3, 5-10 g/ft.sup.3, 5-15 g/ft.sup.3, 5-20
g/ft.sup.3, 10-15 g/ft.sup.3 or 10-20 g/ft.sup.3. In some
embodiments, the overcoat comprises a metal catalyst, such as Pd,
at a concentration of about 5, 10, 15, 20, 50 or 100 g/ft.sup.3. In
some embodiments, the overcoat comprises a metal catalyst, such as
Pd, at a concentration of about 5, 10, 15 or 20 g/ft.sup.3. In
particular embodiments, the overcoat comprises a metal catalyst,
such as Pd, at a concentration of 5, 10, 15 or 20 g/ft.sup.3.
[0164] In some embodiments, the washcoat comprises a metal
catalyst, such as Pd, at a concentration between about 0-50
g/ft.sup.3, 0-30 g/ft.sup.3, 0-20 g/ft.sup.3, 0-15 g/ft.sup.3, 0-10
g/ft.sup.3, 0-5 g/ft.sup.3, 5-10 g/ft.sup.3, 5-15 g/ft.sup.3, 5-20
g/ft.sup.3, 10-15 g/ft.sup.3 or 10-20 g/ft.sup.3. In some
embodiments, the washcoat comprises a metal catalyst, such as Pd,
at a concentration of about 5, 10, 15, 20, 50 or 100 g/ft.sup.3. In
some embodiments, the washcoat comprises a metal catalyst, such as
Pd, at a concentration of about 5, 10, 15 or 20 g/ft.sup.3. In
particular embodiments, the washcoat comprises a metal catalyst,
such as Pd, at a concentration of 5, 10, 15 or 20 g/ft.sup.3.
[0165] In some embodiments, the catalyst system contains a total
amount of metal catalyst, such as Pd, of about 5-200 g/ft.sup.3,
5-100 g/ft.sup.3, 50-100 g/ft.sup.3, 5-50 g/ft.sup.3, 5-20
g/ft.sup.3, or 5-10 g/ft.sup.3. In other embodiments, the catalyst
system contains a total amount of metal catalyst, such as Pd, of
about 5-100 g/ft.sup.3, 5-20 g/ft.sup.3, or 5-10 g/ft.sup.3. In
particular embodiments, the catalyst system contains a total amount
of metal catalyst, such as Pd, of about 5, 10, 15, 20, 50 or 100
g/ft.sup.3. In particular embodiments, the catalyst system contains
a total amount of metal catalyst, such as Pd, of 5, 10, 15, 20, 50
or 100 g/ft.sup.3. The total amount of metal catalyst may be
distributed evenly or unevenly between the washcoat and overcoat
(if present).
[0166] In some embodiments, the catalyst system contains a total
amount of metal catalyst, such as Pd, of up to about 5-200
g/ft.sup.3, 5-100 g/ft.sup.3, 50-100 g/ft.sup.3, 5-50 g/ft.sup.3,
5-20 g/ft.sup.3, or 5-10 g/ft.sup.3. In other embodiments, the
catalyst system contains a total amount of metal catalyst, such as
Pd, of up to about 5-100 g/ft.sup.3, 5-20 g/ft.sup.3, or 5-10
g/ft.sup.3. In some embodiments, the catalyst system contains a
total amount of metal catalyst, such as Pd, of up to about 5, 10,
15, 20, 50 or 100 g/ft.sup.3. In particular embodiments, the
catalyst system contains a total amount of metal catalyst, such as
Pd, of up to 5, 10, 15, 20, 50 or 100 g/ft.sup.3.
[0167] In embodiments wherein both a washcoat and overcoat are
present, the metal catalyst, such as Pd, may be distributed between
the washcoat and overcoat in any proportion. For example, and
without limitation, in embodiments wherein a total of about 20
g/ft.sup.3 of a metal catalyst, such as Pd, is present in the
catalyst system: 1) the washcoat may contain about 15 g/ft.sup.3 of
Pd and the overcoat may contain about 5 g/ft.sup.3 of Pd; 2) the
washcoat may contain about 10 g/ft.sup.3 of Pd and the overcoat may
contain about 10 g/ft.sup.3 of Pd; or 3) the washcoat may contain
about 5 g/ft.sup.3 of Pd and the overcoat may contain about 15
g/ft.sup.3 of Pd. In addition, for example, in embodiments wherein
a total of about 100 g/ft.sup.3 of a catalyst, such as Pd, is
present in the catalyst system, the washcoat and overcoat may each
contain about 50 g/ft.sup.3 of Pd.
[0168] In a particular embodiment, the catalyst system contains a
total of 20 g/ft.sup.3 of Pd wherein 5 g/ft.sup.3 of Pd is present
in the overcoat and 15 g/ft.sup.3 of Pd is present in the washcoat.
In some embodiments, the 5 g/ft.sup.3 of Pd is present in the
overcoat is present as a SS Pd-IWCP OSM.
[0169] It has been found, as is further discussed herein, that the
uneven distribution of the catalyst, such as Pd, between the
washcoat and overcoat can improve the overall performance of the
catalyst system. For example, placing more than half the Pd present
in the catalyst system in the washcoat has been shown to improve
resistance to simultaneous thermal and phosphorus poisoning. This
effect is manifested by an improvement in the OSC of the catalyst
system after aging (see Example 17, Table 13). The benefit of
placing the majority of the Pd in the washcoat likely stems from
the susceptibility of Pd to phosphorus poisoning. Because
phosphorus poisoning is more prevalent at the exterior of the
catalyst (i.e., within the overcoat), the placement of the majority
of Pd in the washcoat protects the metal. Thus, distribution of Pd
in this manner is particularly beneficial in the context of CC
catalysts due to the high exposure of such catalysts to phosphorus
in engine exhaust.
[0170] In some embodiments comprising a CC and UF catalyst, the
total amount of metal catalyst present in a CC catalyst is higher
than the total amount of metal catalyst present in an UF catalyst.
For example, in such embodiments, the total amount of Pd present in
a CC catalyst would be more than the total amount of Pd and/or Rh
(if Rh is present) present in the UF catalyst.
Support Oxides
[0171] Support oxides (mixed metal oxides) are, generally, porous
solid oxides which are used to provide a high surface area which
aids in oxygen distribution and exposure of catalysts to reactants
such as NO.sub.x, CO, and hydrocarbons. Support oxides are normally
stable at high temperatures as well as at a range of reducing and
oxidizing conditions.
[0172] Metal catalysts present in the washcoat, overcoat (if one is
present), or both, are typically supported by support oxides.
However, as discussed herein, in some embodiments, the washcoat
and/or overcoat (if one is present) contains a catalyst, but does
not contain a support oxide. In such embodiments, the washcoat
and/or overcoat present in a CC and/or UF catalyst may contain a SS
Pd-OSM which supports a metal catalyst without the need for a
support oxide. The SS Pd-OSMs are preferably found in the CC
catalyst. Thus, in one embodiment, the present invention
contemplates a CC catalyst which comprises: 1) a washcoat which
comprises, inter alia, a catalyst and a support oxide; and 2) an
overcoat which comprises, inter alia, a catalyst present in a SS
Pd-OSM, and no support oxide. In another embodiment, the present
invention contemplates an UF catalyst comprising a washcoat and an
overcoat wherein both comprise, inter alia, a catalyst and a
support oxide.
[0173] The amount of support oxide present in a catalyst system may
vary depending on where in the system the support oxide is present.
In some embodiments, the washcoat and overcoat (if one is present)
of a catalyst system may contain the same amount of support oxide.
In other embodiments, the washcoat and overcoat (if one is present)
of a catalyst system may contain different amounts of support
oxide.
[0174] Suitable compounds for use as support oxides include, but
are not limited to, gamma-alumina, ceria-based powders, or any
mixture of titania, silica, alumina (transition and alpha-phase),
ceria, zirconia, Ce.sub.1-.alpha.Zr.sub..alpha.O.sub.2, and any
possible doped ceria formulations. In a preferred embodiment, the
support oxide is alumina.
[0175] Modifiers may optionally be added to the alumina to retard
undesired phase transitions of the alumina from the gamma phase to
the alpha phase when the alumina is exposed to elevated
temperatures--i.e., to stabilize the alumina. Examples of suitable
modifiers (or thermal stabilizers) include, for example, rare earth
oxides, silicon oxides, oxides of Group IVB metals (zirconium,
hafnium, or titanium), alkaline earth oxides, or combinations
thereof. Alumina is typically utilized in the washcoat as a high
surface area carrier solid or support and is referred to as "gamma
alumina" or "activated alumina." Suitable alumina compositions
generally have a BET (Brunauer, Emmett and Teller) surface area of
60 m.sup.2/g or more and, often, about 200 m.sup.2/g or more.
[0176] Specific examples of suitable stabilizing agents include
lanthanide oxides (Ln.sub.2O.sub.3) and/or strontium oxide (SrO).
Such lanthanide- and strontium-based stabilizing agents are
typically added to support oxides (e.g., alumina) as a solution of
lanthanide nitrate, strontium nitrate, or mixtures thereof. Heating
or calcining the lanthanide nitrate and/or strontium nitrate then
forms the desired oxide. A particular example of a useful
stabilized alumina is La--Al.sub.2O.sub.3.
[0177] In some embodiments, the washcoat contains alumina as the
support oxide. In particular embodiments, the support oxide is
comprised of La--Al.sub.2O.sub.3. Accordingly, in some embodiments,
the alumina (e.g., La--Al.sub.2O.sub.3) present in the washcoat
constitutes 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%,
14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%,
27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%,
40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%,
53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%,
66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%,
79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%,
92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100% of the washcoat by
weight. In some embodiments, the alumina constitutes about 10-100%
of the washcoat by weight. In other embodiments, the alumina
constitutes about 20-60%, 30-50% or 35-45% of the washcoat by
weight. In other embodiments, the alumina constitutes about 40-80%,
50-70% or 55-65% of the washcoat by weight. In some embodiments,
the alumina constitutes about 20%, 40% or 60% of the washcoat by
weight. In particular embodiments, the alumina constitutes 20%, 40%
or 60% of the washcoat by weight. Such alumina amounts are suitable
for Pd-MPC washcoats.
[0178] The alumina present in the washcoat may also constitute up
to 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%,
15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%,
28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%,
41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%,
54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%,
67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%,
80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%,
93%, 94%, 95%, 96%, 97%, 98%, 99% or 100% of the washcoat by
weight. In some embodiments, the alumina constitutes up to about
10-100% of the washcoat by weight. In other embodiments, the
alumina constitutes up to about 20-60%, 30-50% or 35-45% of the
washcoat by weight. In other embodiments, the alumina constitutes
up to about 40-80%, 50-70% or 55-65% of the washcoat by weight. In
some embodiments, the alumina constitutes up to about 20%, 40% or
60% of the washcoat by weight. In particular embodiments, the
alumina constitutes up to 20%, 40% or 60% of the washcoat by
weight. Such alumina amounts are suitable for Pd-MPC washcoats.
[0179] In some embodiments, the alumina (e.g., La--Al.sub.2O.sub.3)
present in the overcoat (if present) constitutes 1%, 2%, 3%, 4%,
5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%,
19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%,
32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%,
45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%,
58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%,
71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%,
84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%,
97%, 98%, 99% or 100% of the overcoat by weight. In some
embodiments, the alumina constitutes about 0-40% of the overcoat by
weight. In other embodiments, the alumina constitutes about 0-5%,
0-10%, 0-15%, 5-10%, 5-15%, 5-20%, 10-20%, 10-15% or 0-20% of the
overcoat by weight. In other embodiments, the alumina constitutes
about 10-40%, 15-35% or 20-30% of the overcoat by weight. In yet
other embodiments, the alumina constitutes about 40-80%, 50-70%,
55-65%, 60-100%, 70-90%, or 75-85% of the overcoat by weight. In
other embodiments, the alumina constitutes about 0%, 5%, 10%, 15%,
20%, 25%, 40%, 60%, or 80%, of the overcoat by weight. In yet other
embodiments, the alumina constitutes about 0%, 10%, 25%, 40%, 60%,
or 80% of the overcoat by weight. In particular embodiments, the
alumina constitutes 0%, 10%, 25%, 40%, 60%, or 80% of the overcoat
by weight. Such alumina amounts are suitable for Pd-MPC overcoats.
Alumina amounts suitable for SS Pd-OSM overcoats are discussed in
the context of overcoats, above.
[0180] The alumina present in the overcoat may also constitute up
to 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%,
15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%,
28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%,
41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%,
54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%,
67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%,
80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%,
93%, 94%, 95%, 96%, 97%, 98%, 99% or 100% of the overcoat by
weight. In some embodiments, the alumina constitutes up to about
0-40% of the overcoat by weight. In other embodiments, the alumina
constitutes up to about 0-5%, 0-10%, 0-15%, 5-10%, 5-15%, 5-20%,
10-20%, 10-15% or 0-20% of the overcoat by weight. In other
embodiments, the alumina constitutes up to about 10-40%, 15-35% or
20-30% of the overcoat by weight. In yet other embodiments, the
alumina constitutes up to about 40-80%, 50-70%, 55-65%, 60-100%,
70-90%, or 75-85% of the overcoat by weight. In other embodiments,
the alumina constitutes up to about 0%, 5%, 10%, 15%, 20%, 25%,
40%, 60%, or 80%, of the overcoat by weight. In yet other
embodiments, the alumina constitutes up to about 0%, 10%, 25%, 40%,
60%, or 80% of the overcoat by weight. In particular embodiments,
the alumina constitutes up to 0%, 10%, 25%, 40%, 60%, or 80% of the
overcoat by weight. Such alumina amounts are suitable for Pd-MPC
overcoats. Alumina amounts suitable for SS Pd-OSM overcoats are
discussed in the context of overcoats, above.
Oxygen Storage Materials (OSMs)
[0181] During operation, catalytic converters may be exposed to
exhaust that is either rich (contains a high amount of unburnt fuel
compared to oxygen) or lean (contains a low amount of unburnt fuel
compared to oxygen). Accordingly, washcoats and/or overcoats of
catalyst systems may contain oxygen storage materials (OSMs) which
supply oxygen to rich exhaust and take up oxygen from lean exhaust,
buffering the catalyst systems against the fluctuating supply of
oxygen and, in turn, increasing catalyst efficiency with respect to
hydrocarbon and CO oxidation. Thus, OSMs present in, for example,
TWC catalyst compositions, allow the conversion efficiency of the
catalysts system to remain relatively constant even in the face of
varying inlet air/fuel ratios. In some embodiments, the OSM
maintains the air/fuel ratio at the stoichiometric point. OSMs may
comprise zirconia, lanthanides, alkaline earth metals, transition
metals, cerium oxide materials, or mixtures thereof. The use of
cerium oxide in catalytic converters is described in "Critical
Topics in Exhaust Gas Treatment" (Research Studies Press Ltd,
Baldock, Hertfordshire, England, 2000), which is incorporated
herein by reference in its entirety.
[0182] Traditionally, OSMs comprising cerium oxide have a
composition according to the formula:
Ce.sub.1-.alpha.Zr.sub.aO.sub.2-.delta., wherein: [0183]
0<a<1; and [0184] .delta. is an oxygen deficiency valued
between 0.ltoreq..delta.1.ltoreq.(1-a)/2. The oxygen deficiency in
the formula of the cerium oxide-based material changes as the
cerium oxide-based material takes up and releases oxygen.
[0185] In some embodiments, "a" is in the range of approximately
0.07 to approximately 0.70. In other embodiments, "a" is in the
range of approximately 0.15 to approximately 0.53. In yet other
embodiments, "a" is in the range of approximately 0.15 to
approximately 0.28. Typical OSM compositions are described in, for
example, U.S. Pat. No. 7,641,875, which is incorporated herein by
reference in its entirety.
[0186] As discussed above, the present invention refers to improved
OSMs wherein the catalyst (e.g., Pd) is present as a SS within the
OSM. Thus, in some embodiments, the OSM is a SS Pd-OSM.
[0187] The OSM used in a catalyst system (i.e., traditional OSM or
SS Pd-OSM) may vary depending on the location of the OSM. The
identity of the OSM may depend, for example, on whether the OSM is
present in a CC or UF catalyst and may further depend on whether
the OSM is present in the overcoat or washcoat of the CC or UF
catalyst. The SS Pd-OSM may be used in either the overcoat or
washcoat of both the CC and UF catalysts. In some embodiments,
however, the SS Pd-OSM is present only in the CC catalyst. In other
embodiments, the SS Pd-OSM is present in the overcoat of the CC
catalyst, but not in the washcoat. In a particular embodiment, the
SS Pd-OSM present in the overcoat of the CC catalyst, but not in
the washcoat, is a SS Pd-IWCP OSM.
[0188] In some embodiments, the OSM present in the washcoat
constitutes 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%,
14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%,
27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%,
40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%,
53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%,
66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%,
79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%,
92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100% of the washcoat by
weight. In some embodiments, the OSM constitutes about 10-100% of
the washcoat by weight. In other embodiments, the OSM constitutes
about 20-60%, 30-50% or 35-45% of the washcoat by weight. In other
embodiments, the OSM constitutes about 40-80%, 50-70% or 55-65% of
the washcoat by weight. In some embodiments, the OSM constitutes
about 40% or 60% of the washcoat by weight. In particular
embodiments, the OSM constitutes 40% or 60% of the washcoat by
weight.
[0189] The OSM present in the washcoat may also constitute up to
1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%,
16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%,
29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%,
42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%,
55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%,
68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%,
81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,
94%, 95%, 96%, 97%, 98%, 99% or 100% of the washcoat by weight. In
some embodiments, the OSM constitutes up to about 10-100% of the
washcoat by weight. In other embodiments, the OSM constitutes up to
about 20-60%, 30-50% or 35-45% of the washcoat by weight. In other
embodiments, the OSM constitutes up to about 40-80%, 50-70% or
55-65% of the washcoat by weight. In some embodiments, the OSM
constitutes up to about 40% or 60% of the washcoat by weight. In
particular embodiments, the OSM constitutes up to 40% or 60% of the
washcoat by weight.
[0190] In some embodiments, the OSM present in the overcoat (if
present) constitutes 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%,
12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%,
25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%,
38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%,
51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%,
64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%,
77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%,
90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100% of the
overcoat by weight. In some embodiments, the OSM constitutes about
20-80% or 50-100% of the overcoat by weight. In other embodiments,
the OSM constitutes about 20-60%, 30-50%, 35-45%, 50-90%, 60-80%,
65-85%, or 65-75% of the overcoat by weight. In other embodiments,
the OSM constitutes about 40-80%, 50-70%, 55-65%, 60-100%, 70-90%,
or 75-85% of the overcoat by weight. In some embodiments, the OSM
constitutes about 40%, 60%, 70%, 75% or 80% of the overcoat by
weight. In particular embodiments, the OSM constitutes 40%, 60%,
70%, 75% or 80% of the overcoat by weight.
[0191] The OSM present in the overcoat (if present) may also
constitute up to 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%,
13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%,
26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%,
39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%,
52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%,
65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%,
78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%,
91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100% of the overcoat
by weight. In some embodiments, the OSM constitutes up to about
20-80% or 50-100% of the overcoat by weight. In other embodiments,
the OSM constitutes up to about 20-60%, 30-50%, 35-45%, 50-90%,
60-80%, 65-85%, or 65-75% of the overcoat by weight. In other
embodiments, the OSM constitutes up to about 40-80%, 50-70%,
55-65%, 60-100%, 70-90%, or 75-85% of the overcoat by weight. In
some embodiments, the OSM constitutes up to about 40%, 60%, 70%,
75% or 80% of the overcoat by weight. In particular embodiments,
the OSM constitutes up to 40%, 60%, 70%, 75% or 80% of the overcoat
by weight.
[0192] In some embodiments, the overcoats of the present invention
are composed predominantly or entirely of a SS Pd-OSM, such as SS
Pd-IWCP OSM. In some embodiments, the SS Pd-OSM is the only OSM
present in the overcoat and constitutes 1%, 2%, 3%, 4%, 5%, 6%, 7%,
8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%,
22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%,
35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%,
48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%,
61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%,
74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%,
87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or
100% of the overcoat by weight. In some embodiments, the SS Pd-OSM
constitutes about 10-100% of the overcoat by weight. In other
embodiments, the SS Pd-OSM constitutes about 50-100%, 50-90%,
60-80%, 65-75%, or 70-80% of the overcoat by weight. In other
embodiments, the SS Pd-OSM constitutes about 70% or 75% of the
overcoat by weight. In particular embodiments, the SS Pd-OSM
constitutes 70% or 75% of the overcoat by weight.
[0193] The SS Pd-OSM, such as SS Pd-IWCP OSM, present in the
overcoat may also constitute up to 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%,
9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%,
22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%,
35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%,
48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%,
61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%,
74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%,
87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or
100% of the overcoat by weight. In some embodiments, the SS Pd-OSM
constitutes up to about 10-100% of the overcoat by weight. In other
embodiments, the SS Pd-OSM constitutes up to about 50-100%, 50-90%,
60-80%, 65-75%, or 70-80% of the overcoat by weight. In other
embodiments, the SS Pd-OSM constitutes up to about 70% or 75% of
the overcoat by weight. In particular embodiments, the SS Pd-OSM
constitutes up to 70% or 75% of the overcoat by weight.
[0194] In other embodiments, the overcoat comprises 10-100 g/L of
SS Pd-OSM. In other embodiments, the overcoat comprises 50-100 g/L,
50-90 g/L, 60-80 g/L, 65-75 g/L, or 70-80 g/L of SS Pd-OSM. In
other embodiments, the overcoat comprises about 70 g/L of SS
Pd-OSM. In particular embodiments, the overcoat comprises 70 g/L of
SS Pd-OSM.
[0195] In yet other embodiments, the overcoat comprises up to
10-100 g/L of SS Pd-OSM. In other embodiments, the overcoat
comprises up to 50-100 g/L, 50-90 g/L, 60-80 g/L, 65-75 g/L, or
70-80 g/L of SS Pd-OSM. In other embodiments, the overcoat
comprises about up to 70 g/L of SS Pd-OSM. In particular
embodiments, the overcoat comprises up to 70 g/L of SS Pd-OSM.
[0196] In some embodiments, the SS Pd-OSM, such as SS Pd-IWCP OSM,
is present in the washcoat at the same concentration(s) recited in
the context of the overcoat, above. In general, higher amounts of
the SS Pd-OSM are present in the washcoat when compared to the
overcoat.
[0197] In some embodiments, the overcoat and washcoat contain the
following OSMs: washcoat OSM of (30% CeO.sub.2, 60% ZrO.sub.2, 5%
Nd.sub.2O.sub.3 and 5% Y.sub.2O.sub.3) (% by weight) and an
overcoat OSM of (30% CeO.sub.2, 60% ZrO.sub.2, 5% Nd.sub.2O.sub.3,
5% Pr.sub.6O.sub.n) (% by weight).
Methods of Making SS Pd-OSMs
[0198] In yet another aspect, the present invention relates to
methods of making the SS Pd-OSMs disclosed herein.
[0199] In order to form a SS suitable for use in SS Pd-OSMs, the
process for the generation of the OSMs must yield Pd which is
uniformly dispersed over the surface of, and throughout the OSM.
Such an OSM structure can be made by dispersing the Pd precursor on
the surface of the OSM as a host oxide. This dispersal permits the
migration of Pd into sites within the OSM structure during the
calcination process via solid state diffusion.
[0200] The SS Pd OSMs of the present invention were generated by an
Improved Wet Chemical Process (IWCP) and the High Temperature
Process (HTP). The IWCP represents an improvement over the
traditional Wet Chemical Process (WCP). Specifically, the IWCP
yields SS Pd-IWCP OSMs with even dispersal of Pd throughout and on
the surface of the OSM (see Examples 8 and 9 and FIGS. 17-18).
[0201] The key differences between the IWCP and the WCP lie in: 1)
the support choice (specifically an OSM material); 2) the base used
to adjust the pH during the IWCP; and 3) the fact that the amount
of base used during the IWCP is linked to the amount of Pd present
as opposed to a target pH of the solution (as in the WCP). Details
of the IWCP can be found in Example 2.
[0202] It had been found that the type of and amount of base used
is particularly important (see Example 2).
In some embodiments, the base used in the IWCP is selected from
tetraalkylammonium hydroxides (e.g., tetraethylammonium hydroxide,
tetramethylammonium hydroxide, tetrapropylammonium hydroxide and
tetrabutylammonium hydroxide), BaO, Ba(OH).sub.2, BaCO.sub.3, SrO,
Sr(OH).sub.2 and SrCO.sub.3. In a particular embodiment, the base
is tetraethylammonium hydroxide.
[0203] In some embodiments, the base and transition metal are
present in a fixed molar ratio. In particular embodiments, the
molar ratio of base to transition metal is between about 1.5:1 and
3.5:1. In other embodiments, the molar ratio is about 3.5:1,
3.25:1, 3:1, 2.75:1, 2.5:1, 2.25:1, 2:1, 1.75:1 or 1.5:1. In
particular embodiments the molar ratio is 2.5:1 or 2.75:1. In
particular embodiments of the methods above, the base is
tetraethylammonium hydroxide and the transition metal is Pd. In
some embodiments, tetraethylammonium hydroxide and Pd are present
in a molar ratio of 2.5:1 or 2.75:1.
[0204] The SS Pd-OSMs of the present invention can also be made
using a high-temperature process (HTP) (i.e., SS Pd-HTP OSMs). The
HTP entails first mixing a Pd chemical precursor and an oxide OSM,
and then spraying the mixture into a hot furnace. In some
embodiments, the Pd chemical precursor is Pd(NO.sub.3).sub.2. In
some embodiments the temperature of the hot zone of the furnace is
greater than 500.degree. C. In some embodiments the temperature of
the furnace is between 300.degree. C. and 500.degree. C.
[0205] SS Pd-OSMs made from either the IWCP or the HTP process
exhibit similar CO and hydrocarbon performance.
[0206] It is noted that other processes may be used to make a SS
Pd-OSM, such as co-precipitation.
Methods of Using SS Pd-OSMs
[0207] Catalyst systems comprising the SS Pd-OSMs of the present
invention, such the SS Pd-IWCP OSM, are useful for a variety of
purposes. As discussed herein, the SS Pd-OSMs may be used in
catalytic converter systems present in, for example,
automobiles.
[0208] Thus, in some embodiments, catalyst systems comprising the
SS Pd-OSMs of the present invention are used to reduce toxic
exhaust gas emissions from internal combustion engines.
Accordingly, the present invention envisions a method of reducing
toxic exhaust gas emissions comprising contacting the gas emissions
with catalyst systems comprising SS Pd-OSMs, such as the SS Pd-IWCP
OSM. The present invention also refers to a method of reducing
toxic exhaust gas emissions by utilizing catalyst systems
comprising SS Pd-OSMs, such as the SS Pd-IWCP OSM (or by
incorporating the same into a catalyst system).
[0209] Catalyst systems comprising the SS Pd-OSMs of the present
invention, such as the SS Pd-IWCP OSM, exhibit improved oxygen flow
as discussed herein. Accordingly, the present invention envisions a
method of increasing oxygen flow through a catalyst system by
utilizing catalyst systems comprising SS Pd-OSMs, such as the SS
Pd-IWCP OSM (or by incorporating the same into a catalyst
system).
[0210] As discussed herein, catalyst systems comprising the SS
Pd-OSMs of the present invention, such as the SS Pd-IWCP OSM,
exhibit improved OSCs. Thus, the present invention envisions a
method of increasing the OSC of a catalyst system by utilizing a SS
Pd-OSM, such as the SS Pd-IWCP OSM (or by incorporating the same
into a catalyst system).
[0211] Catalyst systems comprising the SS Pd-OSMs of the present
invention, such as the SS Pd-IWCP OSM, also improve the lifetime of
PGM catalysts present in the system. For example, the SS Pd-OSMs of
the present invention reduce poisoning of Pd. Thus, in another
aspect, the present invention refers to methods of improving the
lifetime of a PGM catalyst, such as Pd, present in a catalyst
system by utilizing SS Pd-OSMs, such as the SS Pd-IWCP OSM (or by
incorporating the same into a catalyst system).
[0212] Further, catalyst systems comprising the SS Pd-OSMs of the
present invention, such as the SS Pd-IWCP OSM, improve the
light-off performance of a catalyst system, as discussed herein.
Thus, in one aspect, the present invention refers to methods of
improving the light-off performance of a catalyst system by
utilizing SS Pd-OSMs, such as the SS Pd-IWCP OSM, in a catalyst
system (or by incorporating the same into a catalyst system).
[0213] Catalyst systems comprising the SS Pd-OSMs of the present
invention, such as the SS Pd-IWCP OSM, are able to efficiently
purify exhaust without the need for high levels of Rh. Indeed, such
catalyst systems are able to purify exhaust without the use of any
amount of Rh. Thus, in another embodiment, the present invention
refers to a method of reducing the amount of Rh present in a
catalyst system while maintaining catalyst efficiency by utilizing
SS Pd-OSMs, such as the SS Pd-IWCP OSM, in a catalyst system (or by
incorporating the same into a catalyst system). In some
embodiments, the catalyst system used in such methods is completely
free of Rh.
[0214] The present invention also refers to methods of
simultaneously converting a) nitrogen oxides to nitrogen and
oxygen; b) carbon monoxide to carbon dioxide; and c) hydrocarbons
to carbon dioxide and water (i.e., TWC) present in exhaust gas
emissions, comprising contacting the gas emissions with catalyst
systems comprising SS Pd-OSMs, such as the SS Pd-IWCP OSM. The
present invention also refers to a methods for such TWC by
utilizing catalyst systems comprising SS Pd-OSMs, such as the SS
Pd-IWCP OSM (or by incorporating the same into a catalyst
system).
[0215] These and other embodiments of the invention may be further
illustrated in the following non-limiting Examples.
EXAMPLES
Example 1
Generation of Washcoat Using Multiphase Catalyst (MPC)
[0216] The multi-phase catalyst (MPC) washcoats of the present
invention were produced using standard techniques known in the art
(see, for example, U.S. Pat. No. 7,641,875).
[0217] A slurry comprising the OSM, alumina powder and lanthanide
nitrate solution (commercially available as lanthanum nitrate
product code 5248 from Molycorp, Inc., Mountain Pass, Calif.) in
deionized water was generated. The slurry was then milled in a
Szegvari Type IS Atrittor until the rheology was suitable for
coating the support. A cordierite honeycomb support was dipped into
the slurry. Excess slurry was blown from the support with an air
jet. The support was dried in flowing air at room temperature, was
heat-treated in air at about 150.degree. C., and was calcined at
750.degree. C. for 4 hours to yield a MPC composition.
[0218] An aqueous solution of palladium nitrate and barium
carbonate/acetate was prepared and impregnated into the MPC
composition. The impregnated catalyst was dried in flowing air at
room temperature followed by heat-treatment in air at 700.degree.
C. for 4 hours in air.
Example 2
Generation of OSM Using The Improved Wet Chemical Process
(IWCP)
[0219] Oxygen storage materials generated using the Improved Wet
Chemical Process (IWCP) (e.g., SS Pd-IWCP OSMs) contain a metal
catalyst (e.g., Pd) in a solid solution ("SS") with the OSM (in
this case a Ce-containing mixed metal oxide). Thus, OSMs generated
using the IWCP contain a metal catalyst which is evenly dispersed
throughout the OSM and the surface of the OSM.
[0220] In order to form a solid solution suitable for use in OSMs,
the process for the generation of the OSMs must yield Pd which is
uniformly dispersed over the surface of the OSM. Such an OSM
structure can be made by dispersing the Pd precursor on the surface
of the OSM as a host oxide. This dispersal allows for the migration
of Pd into sites within the OSM structure during the calcination
process. It is noted that starting with a highly segregated Pd
precursor on the surface of the OSM (as in the WCP) would not allow
Pd diffusion into the OSM during calcination. Instead, Pd would
agglomerate into large particles on the surface of the OSM.
Accordingly, a solid solution would not be formed.
[0221] The kind of and amount of base used is particularly crucial
for the formation of a solid solution. Use of the incorrect or
amount of base (i.e., use of the standard WCP) can lead to the
undesired formation of Pd, in the form of PdO, agglomerated on the
surface of the OSM. The IWCP addresses this agglomeration issue.
This is demonstrated in FIG. 11.
[0222] The key differences between the IWCP and WCP lie in: 1) the
support choice (specifically an OSM material); 2) the base used to
adjust the pH during the IWCP; and 3) the fact that the amount of
base used during the IWCP is linked to the amount of Pd present as
opposed to a target pH of the solution (as in the WCP). A
comparison of the key differences between the IWCP) and the WCP for
making OSMs is laid out in Table 1.
TABLE-US-00001 TABLE 1 IWCP WCP (Example w/ (Example w/Rh) Pd-OSM
IWCP) Differences Raw Alumina + OSM OSM (30% CeO.sub.2, Different
material (30% CeO.sub.2, 60% 60% ZrO.sub.2, 5% Nd.sub.2O.sub.3,
support ZrO.sub.2, 5% Nd.sub.2O.sub.3 and 5% Pr.sub.6O.sub.11) + Pd
5% Y.sub.2O.sub.3) + Rh Slurry % ~20% ~20% -- solids OC 60 g/L 60
g/L -- loading Timing After milling After milling -- of adding PGM
precursor Base Ammonium hydroxide Tetraethylammonium Choice
hydroxide of base Base Amount of ammonium Amount of base pH value
addition hydroxide added tetraethylammonium oriented vs. determined
by target hydroxide added base pH determined by amount amount of Pd
present: oriented Molar ratio tetraethyammonium hydroxide:
Pd(NO.sub.3).sub.2 = 2.5:1 or 2.75:1
[0223] In a representative IWCP procedure, Pd(NO.sub.3).sub.2 was
added to an aqueous slurry of milled OSM (30% CeO.sub.2, 60%
ZrO.sub.2, 5% Nd.sub.2O.sub.3 and 5% Pr.sub.6O.sub.11).
Tetraethylammonium hydroxide was then added to generate the
IWCP-OSM slurry.
[0224] Separately, La--Al.sub.2O.sub.3 was milled with acetic acid
at a pH of .about.6.0. BaCO.sub.3 was then added to the milled
La--Al.sub.2O.sub.3 and stirred for approximately 5 minutes. The
La--Al.sub.2O.sub.3/BaCO.sub.3 mixture was then added to IWCP-OSM
slurry and the resulting composition was coated on to the washcoat
which was calcined to generate the Pd-OSM IWCP containing catalyst
composition.
[0225] FIG. 12 is a flowchart illustrating this process.
Example 3
Efficiency of SS Pd-IWCP OSM Based on Vehicle Test Results
[0226] The catalytic efficiency of the SS Pd-IWCP OSM generated
using the method of Example 2 was evaluated. In addition, the SS
Pd-IWCP OSM efficiency was compared to that of a Pd-MPC catalyst
generated using the method of Example 1. Both the SS Pd-IWCP OSM
and the Pd-MPC: contained the same amount of Pd, contained only Pd
as the precious metal catalyst, and were evaluated in a
close-coupled system.
[0227] Improved OSC's, such as those exhibited by the SS Pd-OSMs of
the present invention, are particularly useful in high engine speed
environments. This environment is simulated during testing of
catalysts in the US06 high-speed drive cycle Improved OSC's are
especially important in these environments because of the very high
temperatures and space velocities present (see Table 2). In high
engine speed environments such as those in the US06 high-speed
drive cycle, the conversion efficiencies of NO.sub.x, CO and
hydrocarbons are particularly low resulting in increased tailpipe
emissions.
[0228] Table 2 shows the minimum and maximum catalyst temperature
and space velocity a catalyst system is exposed to in standard
(FTP-75) and high engine speed (US06) conditions. Note that space
velocity is the exhaust flow rate measured in
(liters/hour)/(catalyst volume in liters).
TABLE-US-00002 TABLE 2 Temperature and Space Velocity (SV)
Properties for the FTP and US06 Drive Cycles. FTP-75 US06 Property
Min Max Avg Min Max Avg Temp (.degree. C.) 25 777 630 473 886 764
System SV 358 83,800 15,380 2,500 172,800 33,460 (Hours.sup.-1)
[0229] Tailpipe emissions of catalyst systems containing a CC and
UF catalyst were measured during exposure of the catalyst systems
to the FTP-75 and US06 controlled drive cycles. Both tested systems
contained a Pd-MPC as the UF catalyst. The CC catalyst, however,
was varied with one system containing a SS Pd-IWCP OSM CC catalyst
and the other containing a Pd-MPC CC catalyst. The results in Table
3 demonstrate that US06 performance of the Pd-IWCP OSM is superior
to that of the Pd-MPC.
TABLE-US-00003 TABLE 3 Comparison of the SS Pd-IWCP OSM and Pd MPC
catalysts in the FTP-75 and US-06 tests. Catalyst FTP-75 US-06
system NO.sub.x NMHC CO NO.sub.x NMHC CO (CC + UF) (mg/mi) (mg/mi)
(mg/mi) (mg/mi) (mg/mi) (mg/mi) (CC: 6 g SS Pd- 32.6 4.6 1073 192.7
6.1 1135.9 IWCP OSM) + (UF: 3.6 g Pd-MPC) (CC: 6 g 14.0 4.3 353.3
309.4 7.5 974.5 Pd-MPC) + (UF: 3.6 g Pd-MPC)
[0230] In order to demonstrate the effect of the improved OSC of
the SS Pd-IWCP OSMs on engine emissions, NO.sub.x emissions of a SS
Pd-IWCP OSM catalyst system and a Pd-MPC catalyst system were
measured under varying engine speeds and air/fuel mixtures (A/F).
FIG. 13 charts the perturbations in A/F versus time of the
experiment. FIG. 14 charts the levels of NO.sub.x emissions of the
SS Pd-IWCP OSM and standard Pd-MPC catalyst systems versus time.
While NO.sub.x emissions were generally lower for the SS Pd-IWCP
OSM catalyst system, there are particular regions of interest--see,
for example, at about 100 seconds. At these times, it was observed
that the SS Pd-IWCP OSM catalyst system was much better able to
limit NO.sub.x emissions compared to the Pd-based MPC catalyst
system. One possible explanation for the phenomenon at about 100
seconds is demonstrated in FIG. 13. There is a significant lean
perturbation around this time--i.e., when the engine speed is
varied as it is at about 100 seconds, the air/fuel mixture is
particularly lean. Thus, the much improved OSC of the SS Pd-IWCP
OSM catalyst system may play a key role in limiting NO.sub.x
emissions.
Example 4
Efficiency of SS Pd-IWCP OSM in Different Catalyst System
Environments Based on Vehicle Test Results
[0231] The catalytic efficiency of the SS Pd-IWCP OSM was evaluated
as follows. Two catalyst systems were tested. One system contained
a Pd-MPC catalyst impregnated onto a washcoat containing alumina
and an OSM. The other system contained a) an overcoat containing a
SS Pd-IWCP OSM; and b) a Pd-MPC catalyst impregnated onto a
washcoat containing alumina and an OSM. Both catalysts were
evaluated in a close-coupled system.
[0232] The data in Table 4 demonstrate that the SS Pd-IWCP OSM
catalyst system exhibited stable NMHC (non-methane hydrocarbon), CO
and NO.sub.x emissions even after multiple runs. The emissions were
particularly stable when compared to the catalysts system
comprising only the Pd-MPC catalyst as the source of precious metal
catalyst.
TABLE-US-00004 TABLE 4 Comparison of SS Pd-IWCP OSM and Pd-MPC
Catalyst Emissionsin FTP-75 and US-06 tests (UF Catalyst: = 0/12/6
Pd/Rh bi-layer). FTP75 (WM) US-06 (WM) Close-Coupled (mg/mile)
(mg/mile) Catalyst System Run NMHC CO NO.sub.x NMHC CO NO.sub.x
Pd-MPC only 1 8.1 303 9.2 21 1653 52 Washcoat: 2 12.5 585 13.8 27
3559 48 Pd-MPC 3 15.0 414 12.0 N/A N/A N/A impregnated into 160 g/L
Al.sub.2O.sub.3 + OSM (Pd 102.68 g/ft.sup.3) No Overcoat Pd-MPC 1
11.6 325 13.9 20 1367 62 washcoat + Pd- 2 10.0 347 14.3 N/A N/A N/A
IWCP overcoat Washcoat: Pd-MPC impregnated into 100 g/L
Al.sub.2O.sub.3 + OSM (Pd 54.5 g/ft.sup.3) Overcoat: 60 g/L Pd-IWCP
OSM (Pd 54.5 g/ft.sup.3)
Example 5
Effect of SS Pd-IWCP OSM on Catalyst Temperature
[0233] The effect of the SS Pd-IWCP OSM catalyst on catalyst system
temperature was evaluated. Two catalysts were evaluated. The first
contained a Pd-MPC catalyst (containing 6 g of Pd) impregnated onto
a washcoat containing alumina and an OSM. The second contained a)
an overcoat containing a SS Pd-IWCP OSM (containing 3.88 g of Pd);
and b) a Pd-MPC catalyst (containing 6 g of Pd) impregnated onto a
washcoat containing alumina and an OSM. These two catalysts were
evaluated in a CC catalyst system. Each was coupled to the same UF
catalyst containing 12 g/ft.sup.3 Pd and 6 g/ft.sup.3 Rh.
[0234] Two criteria were measured in these experiments: 1) the rate
of temperature increase of the catalyst; and 2) the maximum
temperature of the catalyst. Both catalyst systems were exposed to
FTP and US06 conditions starting from a cold start. The data in
FIG. 15 demonstrate a more rapid temperature rise in the SS Pd-IWCP
OSM system when compared to the Pd-MPC catalyst--even though the
Pd-OSM only systems contained a higher loading of Pd. The increase
in temperature rise was observed in both the CC coupled catalyst
(which contained the SS Pd-IWCP OSM catalyst) as well as in the
coupled UF catalyst (which contained a Pd-MPC catalyst). Thus, the
increase in heating resulting from the SS Pd-IWCP OSM in the CC
catalyst acted to warm the coupled UF catalyst. In addition, there
was an observed increase in the maximum temperature in both the CC
catalyst and the UF catalyst of the SS Pd-IWCP OSM catalyst system.
The increase in rate of temperature increase and maximum
temperature attained is likely attributable to the efficient
catalysis of the exothermic CO oxidation process by the SS Pd-IWCP
OSM.
Example 6
Oxygen Storage Capacity of SS Pd-IWCP OSM
[0235] The OSC of the SS Pd-IWCP OSM catalyst system was evaluated.
As discussed herein, the OSC is a measure of an OSM's ability to
supply oxygen to rich exhaust and take up oxygen from lean exhaust,
thus buffering a catalyst system against the fluctuating supply of
oxygen by maintaining a steady air/fuel ratio. In particular, the
ability of the SS Pd-IWCP OSM catalyst system to buffer the
air/fuel ratio in both lean and rich A/F environments was evaluated
and compared to the OSC of a Pd-MPC catalyst system and the
original equipment manufacturer ("OEM") OSM.
[0236] In one set of experiments, the amount of CO present in the
exhaust was increased from 0 ppm to 8500 ppm (representing a switch
to a rich A/F). In these experiments, a longer delay in observing
an increase in CO in the catalyst environment corresponds with a
higher OSC of the OSM. In another set of experiments, the amount of
O.sub.2 present in the exhaust was increased from 0 ppm to 4200 ppm
(representing a switch to a lean A/F). In these experiments, a
longer delay in observing an increase in O.sub.2 in the catalyst
environment corresponds with a higher OSC of the OSM. In both
experiments, the delay time is measured relative to a system with
no catalyst. The results of these experiments are summarized in
Table 5, below.
[0237] As the data in Table 5 demonstrate, the SS Pd-IWCP OSM
catalyst system demonstrated a substantially better ability to
buffer the air/fuel mixture when compared to the Pd-MPC and OEM
catalyst systems. This is evidenced by the significantly longer
delay times exhibited with the SS Pd-IWCP OSM catalyst system.
TABLE-US-00005 TABLE 5 OSC Delay Times Comparing the Pd-MPC, OEM Pd
and SS Pd-IWCP OSM Catalysts CO No catalyst Sample Delay Time
Sample Type (s) Time (s) (s) 190 Pd (MPC) 842 847 4.8 Std OEM 849
6.8 SS Pd-IWCP 857 14.3 OSM 190 Pd(MPC) 723 731 9.0 Std OEM 733
10.4 SS Pd-IWCP 745 22.7 OSM
Example 7
Effect of Pd Dispersion on OSC
[0238] The OSC of OSMs is dependent on the level of Pd dispersion
throughout the OSM. It has been observed that the OSC increases as
the Pd dispersion level increases.
[0239] The OSC of OSMs generated using the WCP and IWCP was
compared to OSMs containing surface bulk PdO. See FIG. 16. The
IWCP, which allows for the generation of OSMs with highly dispersed
Pd both on the surface and throughout the OSM, yields OSMs (e.g.,
SS Pd-IWCP OSMs) with improved OSCs.
Example 8
Analysis of Solid Solution Pd-OSM Structure via Scanning Electron
Microscopy
[0240] The structure of the Pd-OSM, wherein the Pd is in a solid
solution ("SS"), was analyzed by scanning electron microscopy
(SEM). FIGS. 17-18 illustrate the differences in SS Pd-OSM
structure (i.e., whether Pd is agglomerates or is well dispersed on
the surface of the OSM) based on the method used to generate the SS
Pd-OSM.
[0241] FIGS. 17 and 26 illustrate that Pd is finely dispersed on
the surface of the SS Pd-OSM when the IWCP or HTP is employed. FIG.
18 illustrates that the WCP does not yield an OSM with Pd present
as a SS.
Example 9
Analysis of the SS Pd-IWCP OSM Structure via X-ray Diffraction
[0242] X-ray diffraction was used to evaluate the level of Pd
dispersion on the surface of the SS Pd-IWCP OSM. X-ray diffraction
is used to determine the presence of different crystallographic
phases of Pd. In particular, x-ray diffraction can be used to
measure the expansion or contraction of a host lattice (e.g., the
lattice of the ceria-based OSM) caused by the doping of the lattice
sites with Pd. Bragg's law is used to convert 2-theta peak values
to lattice parameter distances.
[0243] SS Pd-IWCP OSMs with 2%, 5%, and 10% Pd content (doping)
were prepared for evaluation using x-ray diffraction. In addition,
bulk OSM compositions with 2% and 5% Pd content were prepared to
calibrate the SS Pd-IWCP OSM samples. The bulk OSM compositions can
be used to determine the x-ray diffraction pattern for the
segregated phases present in the bulk compositions--i.e., the
segregated Pd (or PdO) and OSM phases. The x-ray diffraction
pattern of the Pd (or PdO) in the bulk compositions is
representative of Pd which is not in solid solution.
[0244] X-ray diffraction plots were generated for the samples
before (i.e., as-made) and after aging in 10% H.sub.2O/N.sub.2 at
900.degree. C. and 1100.degree. C. Pd concentrations were
calculated by measuring the area under the peak located at --54.9
two-theta, developing standard curves from the physical mixture
samples, and subtracting the detected amount of Pd from the nominal
amount in the sample. FIGS. 19 and 20 show the results for as-made
and thermally aged SS Pd-IWCP OSM and bulk OSM (labeled "PdO")
compositions.
[0245] As FIGS. 19 and 20 indicate, the maximum efficiency of Pd
doping occurs at 2% doping levels. When the OSM is doped with 2%
Pd, essentially all of the Pd is incorporated into the solid
solution. Increasing the amount of Pd doping, however, results in
diminishing returns. For example, when the OSM is doped with 5% Pd,
only 2.21% of the Pd is incorporated into the solid solution.
Moreover, when the OSM is doped with 10% Pd, only 4.08% of the Pd
is incorporated into the solid solution.
[0246] Similar results were observed in the context of the aged
catalysts. After aging, OSMs doped with 2% Pd retained 1.32% Pd in
solid solution. Yet, OSMs doped with 5% and 10% Pd, respectively,
retained 1.30% and 3.58% Pd in solid solution. Notably, after
aging, the OSMs retain the majority of the Pd in solid-solution
form.
[0247] In addition to the decreased efficiency of Pd incorporation
into the solid solution, the use of higher amounts of Pd during the
doping process leads to the undesirable formation of PdO particles
on the surface of the OSM. Such particles are formed by the excess
Pd--i.e., the Pd not incorporated into the solid solution.
[0248] FIG. 21 uses a linear fit to calculate the theoretical
maximum amount of Pd that can be incorporated into a solid solution
before and after aging.
[0249] FIG. 22 shows the effect of the amount of Pd doping on the
OSC of the OSM. Doping of amounts of Pd in excess of the solid
solution limit has a relatively minor impact on the OSC, presumably
because the excess Pd forms bulk Pd or PdO particles on the surface
of the OSM.
[0250] FIG. 23 demonstrates the effect of doping small Pd.sup.2+
cations (0.86 .ANG.) onto the Ce.sup.4+ (1.034 .ANG.) sites of the
OSM for a 2% solid solution of Pd in ceria (OSM). As the data
indicates, the doping of the small Pd.sup.2+ cations leads to a
contraction of the lattice consistent with the smaller sized dopant
cation.
Example 10
Mechanism of OSC Improvement with Solid Solution Pd-OSMs
[0251] FIG. 6 illustrates the processes by which Pd doping of the
OSM provides improved OSCs. FIG. 6 shows how Pd.sup.2+ ions occupy
Ce.sup.4+ sites (represented as squares) in the OSM and produce
extra oxygen vacancies. This increases the OSC by providing extra
O.sub.2 storage/release sites. Thus, the doping of the smaller
Pd.sup.2+ ions allows for the easier diffusion of O.sub.2 from the
internal portion of the OSM to the surface of the OSM. This O.sub.2
diffusion results in the formation of an O.sub.2 vacancy (resented
by a "V" in the O.sub.2 binding site (a circle)).
[0252] The combination of a) the increased amount of oxygen
storage/release sites; and b) the improved oxygen diffusion rates
has a multiplicative effect on improving the OSC. This phenomenon
is illustrated in FIG. 7.
Example 11
Improving High-Temperature Performance of SS Pd-IWCP OSMs
[0253] The high-temperature performance of SS Pd-IWCP OSM generated
in Example 2 can be further enhanced in a variety of ways. First,
care can be taken to use a Pd concentration of up to 2% in order to
ensure that the Pd is present as a solid solution. The effect of
the Pd concentration on NO.sub.2 conversion is demonstrated in
Table 6. The data in Table 6 also demonstrates the beneficial
effect of adding alumina to the overcoat in order to maintain Pd
concentration below 2%. The catalytic efficiency was measured after
high-temperature aging at typical USO6 conditions (800.degree. C.
with a Space Velocity of 150,000 hr.sup.-1). All catalysts were
evaluated in a CC system.
TABLE-US-00006 TABLE 6 NO.sub.x Conversion Efficiency at
800.degree. C. and Space Velocity of 150,000 hr.sup.-1 After Aging
at 1000.degree. C. Washcoat Overcoat NO.sub.x % Pd-MPC impregnated
into 60 g/L SS Pd-IWCP OSM 74.0 100 g/L washcoat of alumina + at
2.93% Pd OSM Pd-MPC impregnated into 120 g/L SS Pd-IWCP OSM 76.2
100 g/L washcoat of alumina + at 1.47% Pd OSM Pd-MPC impregnated
into 90 g/L SS Pd-IWCP OSM 82.9 100 g/L washcoat of alumina + at
1.96% Pd + 30 g/L Al.sub.2O.sub.3 OSM
[0254] The effect of adding alumina to overcoats containing SS
Pd-IWCP OSMs on the OSC was also evaluated. Table 7 shows the
beneficial impact of the addition of 25% (by weight) of alumina to
the SS Pd-IWCP OSM overcoat after thermal (at 1000.degree. C.) and
phosphorus aging (2 hours at 700 .degree. C.).
TABLE-US-00007 TABLE 7 The beneficial effect of the presence of
alumina in overcoats containing SS Pd-IWCP OSM. O.sub.2 delay CO
delay time at time at Overcoat layer Washcoat 575.degree. C.
575.degree. C. (50 g/ft.sup.3 Pd) layer (seconds) seconds) 60 g/L
Pd-OSM IWCP 100 g/L WC 17.00 10.04 (thermal aging) with 40% OSM 50
g/ft.sup.3 Pd MPC 120 g/L Pd-OSM 100 g/L WC 23.22 14.30 IWCP + 25%
Al.sub.2O.sub.3 with 40% OSM (thermal aging) 50 g/ft.sup.3 Pd MPC
90 g/L Pd-OSM IWCP + 150 g/L WC 23.70 14.34 25% Al.sub.2O.sub.3
with 40% OSM (thermal aging) 50 g/ft.sup.3 Pd MPC 90 g/L Pd-OSM
IWCP 150 g/L WC 26.21 13.27 (thermal aging) with 40% OSM 50
g/ft.sup.3 Pd MPC 60 g/L Pd-OSM IWCP 100 g/L WC 8.08 2.41 (thermal
aging) with 40% OSM 50 g/ft.sup.3 Pd MPC 120 g/L Pd-OSM 100 g/L WC
10.76 3.62 IWCP + 25% Al.sub.2O.sub.3 with 40% OSM (thermal aging)
50 g/ft.sup.3 Pd MPC 90 g/L Pd-OSM IWCP + 150 g/L WC 10.23 3.38 25%
Al.sub.2O.sub.3 with 40% OSM (thermal aging) 50 g/ft.sup.3 Pd MPC
90 g/L Pd-OSM IWCP 150 g/L WC 9.60 2.81 (thermal aging) with 40%
OSM 50 g/ft.sup.3 Pd MPC
[0255] The effect of adding alumina to overcoats containing SS
Pd-IWCP OSM on phosphorus aging resistance alone was also
evaluated. FIG. 24 illustrates that use of up to 40% by weight
La--Al.sub.2O.sub.3 improves the NO.sub.x performance after
phosphorus aging.
Example 12
Improving Resistance to Phosphorus Aging by Adding BaCO.sub.3 to
the Overcoats Containing SS Pd-IWCP OSMs
[0256] The effect of adding varying amounts of BaCO.sub.3 to
overcoats containing SS Pd-IWCP OSMs was evaluated. In these
experiments the composition of the washcoat remained constant: 50
g/ft.sup.3 of a Pd-MPC catalyst impregnated onto a 100 g/L washcoat
containing alumina and an OSM. The addition of BaCO.sub.3 results
in an improvement in both T90 (temperature at which there is 90%
conversion of exhaust gases) and NO.sub.x conversion efficiency.
The data for a series of catalysts with different overcoat designs
is shown in Table 8. NO.sub.x conversion efficiency was measured at
575.degree. C. with a 0.125 Hz perturbation. Both NO.sub.x
conversion efficiency and T90 values were measured after thermal
aging (1000.degree. C.) and phosphorus aging (700.degree. C.,
2hrs).
TABLE-US-00008 TABLE 8 Effect of BaCO.sub.3 on NO.sub.x Conversion
Efficiency and T90. NO.sub.x % at 575.degree. C. Overcoat layer T90
(0.5 Hz) (.degree. C.) (0.125 Hz) A. 60 g/L SS Pd-IWCP OSM 459.2
50.7 (50 g/ft.sup.3 Pd) B. 60 g/L SS Pd-IWCP OSM 414.0 71.7 (50
g/ft.sup.3 Pd + 30 g/L BaCO.sub.3) C. 60 g/L SS Pd-IWCP OSM 388.5
72.6 (50 g/ft.sup.3 Pd + 20 g/L Ba acetate + 10 g/L La-alumina)
Example 13
Rationale Behind Resistance to Phosphorus Aging by Addition of an
Alkaline Earth and Alumina in a SS Pd-IWCP OSM Overcoat
[0257] The effect of adding BaCO.sub.3 and La.sub.2O.sub.3 on the
stability of overcoats containing SS Pd-IWCP OSMs was evaluated.
FIG. 25 compares the thermodynamic term (log of the reaction
equilibrium between the relevant starting components and
carbonates) for the reaction of BaCO.sub.3, La.sub.2O.sub.3 and
Al.sub.2O.sub.3 (present in the SS Pd-IWCP OSM overcoats) with
P.sub.2O.sub.5 (in the gas stream). La.sub.2O.sub.3 and BaCO.sub.3
improve overcoat function after phosphorus aging by preferentially
reacting with and trapping phosphorus in the exhaust gas stream.
La.sub.2O.sub.3 and BaCO.sub.3 are particularly useful due to the
relative thermodynamic stability of LaPO.sub.4 and
Ba.sub.3(PO.sub.4).sub.2 (formed upon reaction with P.sub.2O.sub.5)
compared to AlPO.sub.4. The phosphorus trapping reduces the
poisoning of the catalyst and, in turn, increases catalyst lifetime
and efficiency.
Example 14
Additional Studies on Improvements to Catalyst Efficiency by
Addition of BaCO.sub.3 in a SS Pd-IWCP OSM Overcoat
[0258] The data in Table 9 illustrate the beneficial effect of the
presence of Ba in the overcoat for NO.sub.x and CO conversion
efficiency after phosphorus aging. Increasing the amount of Ba
improves CO and NOx conversion efficiency while maintaining THC
efficiency.
TABLE-US-00009 TABLE 9 The presence of Ba in the overcoat improves
resistance of the catalyst to phosphorus aging. All samples were
phosphorus-aged for 2 hours before testing. NO.sub.x conversion CO
conversion THC conversion at 575.degree. C. at 575.degree. C. at
575.degree. C. Overcoat layer (0.125 Hz) (0.125 Hz) (0.125 Hz) 60
g/L SS Pd-IWCP 50.7% 68.0% 96.8% OSM (50 g/ft.sup.3 Pd) 60 g/L SS
Pd-IWCP 62.5% 70.6% 97.0% OSM (50 g/ft.sup.3 Pd + 10 g/L BaCO.sub.3
+ 10 g/L La-alumina) 60 g/L SS Pd-IWCP 72.6% 73.6% 97.4% OSM (50
g/ft.sup.3 Pd + 20 g/L BaCO.sub.3 + 10 g/L La-alumina) 60 g/L SS
Pd-IWCP 71.7% 76.8% 96.9% OSM (50 g/ft.sup.3 Pd + 30 g/L
BaCO.sub.3)
[0259] The data in Table 10 illustrate the differences in light-off
temperature for NO.sub.x, CO and THC conversions between catalysts
containing Ba or Ca in the overcoat after phosphorus aging. As
illustrated by the data, the addition of Ba and Ca to the overcoat
improves light-off temperatures.
TABLE-US-00010 TABLE 10 Comparison of light off temperature for
various overcoat compositions. after phosphorus aging (700.degree.
C., 2 hrs). NO.sub.x T90 CO T90 THC T90 Overcoat layer (0.5 Hz)
(0.5 Hz) (0.5 Hz) (50 g/ft.sup.3 Pd) Washcoat layer (.degree. C.)
(.degree. C.) (.degree. C.) 60 g/L Pd-OSM IWCP 100 g/L WC -- --
409.3 with 40% OSM 51 g/ft.sup.3 Pd MPC 120 g/L; 75% Pd-OSM 100
g/LWC 434.2 -- 380.0 IWCP + 25% La- with 40% OSM alumina + 3 g
CaCO.sub.3 50 g/ft.sup.3 Pd MPC 120 g/L; 75% Pd-OSM 100 g/L WC
408.4 419.6 367.2 IWCP + 25% La- with 40% OSM alumina + 15 g
CaCO.sub.3 50 g/ft.sup.3 Pd MPC 120 g/L; 75% Pd-OSM 100 g/L WC
414.2 416.3 353.0 IWCP + 25% La- with 40% OSM alumina + 30 g
CaCO.sub.3 50 g/ft.sup.3 Pd MPC 120 g/L; 75% Pd-OSM 100 g/L WC
362.7 344.1 349.2 IWCP + 25% La- with 40% OSM alumina + 30 g
BaCO.sub.3 50 g/ft.sup.3 Pd MPC 120 g/L; 75% Pd-OSM 100 g/L WC
380.9 338.0 349.4 IWCP + 25% La- with 40% OSM alumina + 60 g
BaCO.sub.3 50 g/ft.sup.3 Pd MPC 120 g/L; 75% Pd-OSM 100 g/L WC
442.3 -- 400.4 IWCP + 25% La- with 40% OSM alumina + 60 g Ba 50
g/ft.sup.3 Pd MPC acetate 120 g/L; 75% Pd-OSM 100 g/L WC 412.9
460.5 389.0 IWCP + 25% La- with 40% OSM alumina + 11% Ba- 50
g/ft.sup.3 Pd MPC Al.sub.2O.sub.3
Example 15
Improved Resistance to Phosphorus Aging by Increasing Washcoat
Thickness
[0260] Table 11 shows NO.sub.x conversion efficiency at 400.degree.
C. as a function of washcoat and overcoat design after thermal and
phosphorus aging. The increase in washcoat thickness from 100 g/L
to 180 g/L has a positive impact on the NO.sub.x conversion
efficiency. The additional surface area of the washcoat layer
enables a higher activity in a location removed from the effects of
the phosphorus aging (as phosphorus aging is seen primarily in the
overcoat).
[0261] Table 11 also shows the improved OSC as the washcoat
thickness is increased from 100 g/L to 180 g/L. The results
indicate that increasing washcoat mass increases OSM content and
function.
TABLE-US-00011 TABLE 11 NO.sub.x conversion Efficiency at
400.degree. C. and OSC delay time (in seconds) after thermal aging
(1000.degree. C.) and Phosphorus aging (700.degree. C., 2 hrs).
NO.sub.x % at CO delay 400.degree. C. time at 575.degree. C.
Overcoat layer (50 g/ft.sup.3 Pd) WC layer (0.5 Hz) (seconds) 60
g/L Pd-OSM IWCP 100 g/L WC 60.6 1.45 with 40% OSM 50 g/ft.sup.3 Pd
MPC 120 g/L; 75% Pd-OSM 100 g/L WC 71.0 3.17 IWCP + 25% La-alumina
with 40% OSM 50 g/ft.sup.3 Pd MPC 120 g/L; 75% Pd-OSM 150 g/L WC
86.1 5.37 IWCP + 25% La-alumina with 40% OSM 50 g/ft.sup.3 Pd MPC
120 g/L; 75% Pd-OSM 180 g/L WC 96.9 6.08 IWCP + 25% La-alumina with
40% OSM 50 g/ft.sup.3 Pd MPC
Example 16
Improved OSC Delay Time After Thermal and Phosphorus Aging in 20
g/ft.sup.3 Pd Only CC Catalyst by Increasing Washcoat Thickness
[0262] Table 12 shows the effect of washcoat thickness on OSC
compared to a reference Pd/Rh CC catalyst. The OSC delay time at
575.degree. C. after thermal aging (1000.degree. C. for 40 hours)
shows an optimal improvement with a washcoat at 180 g/L. The OSC
delay time at 575.degree. C. after thermal (1000.degree. C. for 40
hours) and phosphorus (700.degree. C. for 2 hours) aging improves
with increasing washcoat loading across the whole range examined
(i.e., up to 210 g/L). All catalysts were evaluated in CC catalyst
systems.
TABLE-US-00012 TABLE 12 The effect of washcoat loading on OSC delay
time Relative CO-OSC Relative CO- Delay Time OSC Delay Time
(seconds) after (seconds) after thermal and P- Overcoat layer
Washcoat layer thermal aging aging Reference Catalyst 60 g/L Rh on
La- 180 g/L WC with 40% OSM 1.08 0.91 Al.sub.2O.sub.3 + OSM. 12
g/ft.sup.3 Pd MPC 6 g/ft.sup.3 Rh 70 g/L SS Pd-IWCP 150 g/L WC with
60% OSM 0.49 0.62 OSM + 20 g/L BaCO.sub.3 + 5 g/ft.sup.3 Pd MPC 10
g/L La-Al.sub.2O.sub.3. 15 g/ft.sup.3 Pd 70 g/L SS Pd-IWCP 180 g/L
WC with 60% OSM 0.67 0.61 OSM + 20 g/L BaCO.sub.3 + 5 g/ft.sup.3 Pd
MPC 10 g/L La-Al.sub.2O.sub.3. 15 g/ft.sup.3 Pd 70 g/L SS Pd-IWCP
210 g/L WC with 60% OSM 0.45 1.07 OSM + 20 g/L BaCO.sub.3 + 5
g/ft.sup.3 Pd MPC 10 g/L La-Al.sub.2O.sub.3. 15 g/ft.sup.3 Pd
Example 17
Improved OSC Delay Time After Thermal and Phosphorus Aging in
20g/ft.sup.3 Pd Only CC Catalyst by Optimizing the Partition of Pd
Between the Washcoat and Overcoat Layers
[0263] Table 13 shows the improved OSC as a function of Pd
partitioning between the washcoat and overcoat. Partitioning the Pd
between the washcoat:overcoat in a ratio of 15:5 has a beneficial
impact on OSC after thermal (1000.degree. C. for 40 hours) and
phosphorus (700.degree. C. for 2 hours) aging relative to a Pd
partitioning of 10:10.
TABLE-US-00013 TABLE 13 The effect of Pd partitioning on OSC delay
time CO-OSC Delay Overcoat layer Washcoat layer Time (seconds)
Reference Catalyst 60 g/L Rh on La-Al.sub.2O.sub.3 + 180 g/L WC
with 40% OSM 5.41 OSM. 12 g/ft.sup.3 Pd MPC 6 g/ft.sup.3 Rh. 70 g/L
SS Pd-IWCP 180 g/L WC with 60% OSM 1.96 OSM + 20 g/L BaCO.sub.3 +
10 g/ft.sup.3 Pd MPC 10 g/L La-Al.sub.2O.sub.3. 10 g/ft.sup.3 Pd 70
g/L SS Pd-IWCP 180 g/L WC with 60% OSM 6.49 OSM + 20 g/L BaCO.sub.3
+ 15 g/ft.sup.3 Pd MPC 10 g/L La-Al.sub.2O.sub.3. 5 g/ft.sup.3
Pd
Example 18
Improved OSC Delay Time After Thermal and Phosphorus Aging in 20
g/ft.sup.3 Pd Only CC Catalyst by Increasing the OSM Portion of the
Washcoat
[0264] Table 14 shows the improved OSC delay time attributed to
increasing the OSM portion of the washcoat. Comparison of catalysts
with 60% OSM and 80% OSM in the washcoat shows improved OSC delay
with the 80% OSM washcoat in the washcoat after thermal
(1000.degree. C. for 40 hours) and phosphorus (700.degree. C. for 2
hours) aging.
TABLE-US-00014 TABLE 14 The effect of the OSM fraction present in
the washcoat on OSC delay time CO-OSC Delay Overcoat layer Washcoat
layer Time (seconds) Reference Catalyst 60 g/L Rh on La- 180 g/L WC
with 40% OSM 5.41 Al.sub.2O.sub.3 + OSM. 12 g/ft.sup.3 Pd MPC 6
g/ft.sup.3 Rh 70 g/L SS Pd-IWCP 100 g/L WC with 60% OSM 2.72 OSM +
20 g/L BaCO.sub.3 10 g/ft.sup.3 Pd MPC and 10 g/L
La-Al.sub.2O.sub.3. 10 g/ft.sup.3 Pd 70 g/L SS Pd-IWCP 100 g/L WC
with 80% OSM 3.13 OSM + 20 g/L BaCO.sub.3 10 g/ft.sup.3 Pd MPC and
10 g/L La-Al.sub.2O.sub.3. 10 g/ft.sup.3 Pd
Example 19
Generation OSM Using The High Temperature Process (HTP)
[0265] Oxygen storage materials generated using the High
Temperature Process (e.g., SS Pd-HTP OSMs) contain a metal catalyst
(e.g., Pd) in a solid solution ("SS") with the OSM (in this case a
Ce-containing mixed metal oxide). Thus, OSMs generated using the
HTP contain a metal catalyst which is evenly dispersed throughout
the OSM and the surface of the OSM.
[0266] The HTP entails first mixing a Pd chemical precursor and an
oxide OSM, and then spraying the mixture into a hot furnace. In a
representative experiment, the SS Pd-HTP OSM was generated by 1)
co-milling (30% CeO.sub.2, 60% ZrO.sub.2, 5% Nd.sub.2O.sub.3 and 5%
Pr.sub.6O.sub.11) and a Pd(NO.sub.3).sub.2; and 2) spraying the
resulting mixture of into a furnace.
Example 20
SS Pd-OSMs Generated Using Different Processes Perform
Similarly
[0267] Two different processes were employed to generate the SS
Pd-OSMs of the present invention: 1) an Improved Wet Chemical
Process (IWCP); and 2) High-Temperature Process (HTP).
[0268] The IWCP entails a process described in Example 10. The HTP
entails a process described in Example 19.
[0269] As is seen from FIG. 27, SS Pd-OSMs made from either the
IWCP or the HTP process exhibit similar CO and hydrocarbon
performance.
* * * * *