U.S. patent application number 09/511592 was filed with the patent office on 2002-03-14 for exhaust gas catalyst and method of manufacturing same.
This patent application is currently assigned to Ford Global Technologies, Inc.. Invention is credited to Gandhi, Haren Sakarlal, Graham, George Wade, Jen, Hung-Wen, Shigapov, Albert Nazipovich.
Application Number | 20020032123 09/511592 |
Document ID | / |
Family ID | 24035574 |
Filed Date | 2002-03-14 |
United States Patent
Application |
20020032123 |
Kind Code |
A1 |
Shigapov, Albert Nazipovich ;
et al. |
March 14, 2002 |
Exhaust gas catalyst and method of manufacturing same
Abstract
The present invention involves an exhaust gas catalyst and
method of manufacturing same. The invention provides for a
cost-effective material which lowers the cold-start emissions from
the exhaust of vehicles. The invention is a passive system which
accelerates the light-off temperature of catalyst in a
cost-effective fashion. The invention includes a method of
manufacturing an exhaust gas catalyst capable of lowering
cold-start emissions including the steps of providing an oxide
mixture having praseodymium and cerium, doping about 0-10% weight
zirconium and about 0-10% weight yttrium to the oxide mixture,
adding about 0-2% weight metal including palladium, platinum, or
rhodium to the oxide mixture, mixing gamma aluminum to the oxide
mixture for washcoating and washcoating the oxide mixture onto a
monolithic substrate.
Inventors: |
Shigapov, Albert Nazipovich;
(Krasnoyarsk, RU) ; Graham, George Wade; (Ann
Arbor, MI) ; Gandhi, Haren Sakarlal; (Farmington,
MI) ; Jen, Hung-Wen; (Troy, MI) |
Correspondence
Address: |
Lawrence G Almeda
Brooks & Kushman
1000 Town Center Twenty-Second Floor
Southfield
MI
48075-1351
US
|
Assignee: |
Ford Global Technologies,
Inc.
600 Parklane Towers East
Dearborn
MI
48126
|
Family ID: |
24035574 |
Appl. No.: |
09/511592 |
Filed: |
February 23, 2000 |
Current U.S.
Class: |
502/304 ;
502/182; 502/185 |
Current CPC
Class: |
B01J 23/10 20130101;
B01D 53/945 20130101; B01J 37/0215 20130101; Y02T 10/22 20130101;
Y02T 10/12 20130101; Y02A 50/2324 20180101; B01J 23/63 20130101;
Y02A 50/20 20180101 |
Class at
Publication: |
502/304 ;
502/182; 502/185 |
International
Class: |
B01J 023/10 |
Claims
What is claimed is:
1. A method of manufacturing an exhaust gas catalyst capable of
lowering cold-start emissions, the method comprising: providing an
oxide mixture of praseodymium and cerium; doping the oxide mixture
with 0-10 wt % zirconium and 0%-10 wt % yttrium; doping the oxide
mixture with 0-2 wt % precious metal; mixing gamma alumina to the
oxide mixture for washcoating; and washcoating the mixture onto a
monolithic substrate.
2. The method of claim 1 wherein the oxide mixture has praseodymium
and cerium in substantially equal molar content.
3. The method of claim 1 wherein the step of doping further
comprises doping about 0-2 wt % zirconium and about 0-2 wt %
yttrium to the oxide mixture.
4. The method of claim 1 wherein the step of doping further
comprises doping about 0.1-1.5 wt % precious metal to the oxide
mixture.
5. The method of claim 4 wherein the step of doping the precious
metal occurs immediately after the step of doping the zirconium and
yttrium to the oxide material.
6. The method of claim 1 wherein gamma alumina is mixed with the
oxide mixture at a ratio of 0.1-1 mole of gamma alumina to the
oxide mixture.
7. The method of claim, wherein the precious metal is selected from
the group consisting of platinum, rhodium, palladium, and mixtures
thereof.
8. An exhaust gas catalyst supported on a monolithic substrate, the
catalyst capable of lowering cold-start emissions, the catalyst
comprising: an oxide mixture washcoated on the monolithic
substrate, the oxide mixture having substantially equal molar
content of praseodymium and cerium, about 0-10 wt % zirconium and
about 0-10 wt % yttrium, and about 0-2 wt % precious metal.
9. A method of manufacturing an exhaust gas catalyst capable of
lowering cold-start emissions, the method comprising: providing an
oxide mixture of praseodymium and cerium; doping the oxide mixture
with 0-10 wt % zirconium, 0%-10 wt % yttrium, and 0-2 wt % precious
metal; mixing gamma alumina to the oxide mixture for washcoating;
and washcoating the mixture onto a monolithic substrate, whereby
providing praseodymium increases oxygen storage capacity of the
catalyst and decreases a required amount of the precious metal
doped to the oxide mixture of the catalyst.
Description
TECHNICAL FIELD
[0001] This invention relates to an exhaust gas catalyst capable of
lowering cold-start emissions and a method of manufacturing the
exhaust gas catalyst.
BACKGROUND ART
[0002] The need to lower vehicle exhaust emissions continues to
create challenges, especially in the wake of stringent
environmental regulations. The need to lower cold-start emissions
is at the heart of most emissions reduction strategy, since
cold-start emissions account for a significant portion of exhaust
emissions from any given vehicle. During startup, hydrocarbons can
be passed through the exhaust system before the catalyst can heat
up and convert the hydrocarbons to more desirable gases. Although a
large portion of hydrocarbons are reduced, an amount of
hydrocarbons and other undesirable gases may be allowed to pass
through the exhaust system without reduction thereof.
[0003] One solution to the cold-start emission problem is providing
a material that is able to give off oxygen to the catalyst during
startup conditions such that the "light-off" temperature of the
catalyst is accelerated. The light-off temperature is the
temperature at which the catalyst reacts with hydrocarbons and
other exhaust gases to reduce these gases, which are undesirable,
to more desirable gases such as carbon dioxide. Oxygen, when fed to
the catalyst, creates an exothermic reaction to the catalyst,
resulting in increased temperature which allows the catalyst to
reach the light-off temperature more quickly.
[0004] Currently, palladium is used with a cerium-zirconium mixed
oxide support, an aluminum oxide support, or a mixture thereof to
give off oxygen at startup conditions (low temperature), in order
to accelerate light-off of the catalyst. However, palladium is an
extremely expensive material which typically contributes to
approximately 95% of the total cost of the catalyst. Recent studies
have thus focused on methods and materials to reduce the
consumption of palladium while providing an effective means for
accelerating the light-off temperature of the catalyst.
[0005] The use of additional hardware has also been proposed to
solve the cold-start problem. In some cases, the additional
hardware allows the exhaust system catalyst to be heated directly
in order to accelerate light-off of the catalyst. For example, an
electrically heated catalyst may be used where the catalyst is
heated directly by an electric heater. Prior to startup, current is
run through the heater via the vehicle battery, and the heat
produced accelerates light-off of the catalyst and, in turn, lowers
the cold-start emissions.
[0006] Another example of an active approach is to allow fuel to
combust near the catalyst to quickly raise the temperature thereof.
This is accomplished by running lines and having an ignition system
disposed on the vehicle. Generally, systems that incorporate
additional hardware, such as the examples mentioned above, result
in high costs for implementation.
[0007] Thus, what is needed is a cost effective solution to the
cold-start emissions problem.
DISCLOSURE OF INVENTION
[0008] Accordingly it is an object of the present invention to
provide a cost effective material which lowers the cold-start
emissions from the exhaust of vehicles.
[0009] It is another object of the present invention to provide a
passive system which accelerates the light-off temperature of
catalysts in a cost-effective fashion.
[0010] Yet another object of this invention is to provide a method
of manufacturing an exhaust gas catalyst capable of lowering
cold-start emissions through a three-way catalyst including mixed
metal oxides.
[0011] The method provides an exhaust gas catalyst having an oxide
mixture with substantially equal molar content of praseodymium and
cerium, doping about 0 to 10 weight % zirconium and about 0-10
weight % yttrium to the oxide mixture, and adding or doping about
0-2 weight % precious metal including palladium, platinum, or
rhodium to the oxide mixture. The method further involves mixing
gamma alumina to the oxide mixture for washcoating, and washcoating
the mixture onto a monolithic substrate.
[0012] Another specific object of this invention is an exhaust gas
catalyst supported on a monolithic substrate in which the catalyst
is capable of lowering cold-start emissions. The catalyst comprises
an oxide mixture which is washcoated on the monolithic substrate.
The oxide mixture has substantially equal molar content of
praseodymium and cerium. The oxide mixture also has about 0 to 10
weight % zirconium and about 0-10 weight % yttrium, and about 0-2
weight % precious metal which includes palladium, platinum, or
rhodium.
[0013] In another object of this invention provides for a method of
manufacturing an exhaust gas catalyst capable of lowering
cold-start emissions through a three-way catalyst including mixed
metal oxides.
[0014] The method provides an exhaust gas catalyst having an oxide
mixture of praseodymium and cerium, doping about 0 to 10 weight %
zirconium, about 0-10 weight % yttrium to the oxide mixture, and
about 0-2 weight % precious metal including palladium, platinum, or
rhodium to the oxide mixture. The method further involves mixing
gamma alumina to the oxide mixture for washcoating, and washcoating
the mixture onto a monolithic substrate.
[0015] In yet another embodiment of the invention, a method of
making an oxygen storage material for automotive exhaust catalysts
is provided wherein oxygen storage materials having a low
temperature of oxygen release, such as praseodymia can be made
thermally stable by an organic-templating method that incorporates
low levels of zirconia, yttria and possibly other additives.
BRIEF DESCRIPTION OF DRAWINGS
[0016] FIG. 1 is a table which shows the effect of surface area of
mixed oxides as concentration of zirconium is increased in an equal
molar concentration mixture of praseodymia and ceria;
[0017] FIG. 2 is another table which shows the effect of oxygen
storage capacities of mixed oxides as the concentration of
zirconium is increased in an equal molar concentration mixture of
praseodymia and ceria;
[0018] FIG. 3 is a graph which shows the oxygen storage capacities
of mixed oxides having praseodymia verus mixed oxides without
praseodymia; and
[0019] FIG. 4 is a bar graph which shows the oxygen storage
capacities of mixed oxides having praseodymia and adding precious
metal at the time the mixed oxide is made versus mixed oxides
without praseodymia.
BEST MODE FOR CARRYING OUT THE INVENTION
[0020] The invention is a method for manufacturing an exhaust gas
catalyst capable of lowering cold-start emission. More
specifically, the method teaches the formation of high surface
area, thermally stable oxygen storage materials for automotive
exhaust catalysts. The method generally includes providing an oxide
mixture having praseodymium and cerium, doping about 0-10 weight %
zirconium and about 0-10 weight % yttrium to the oxide mixture, and
adding about 0-2 weight % precious metal to the oxide mixture. The
precious metal may include palladium, platinum, rhodium or mixture
thereof. The method generally further includes mixing gamma alumina
to the oxide mixture for washcoating and washcoating the mixture
onto a monolithic substrate. As a result, a material may be
manufactured that lowers cold-start emissions. The resulting
material is an exhaust gas catalyst supported on a monolithic
substrate in which the catalyst comprises a praseodymium-cerium
oxide mixture washcoated on the monolithic substrate.
[0021] Throughout the specification, the term "oxide mixture" or
"mixed oxide" refers to a solid solution mixed oxide, or alloy,
rather than a physical mixture of single oxides.
[0022] A surprising and unexpected advantage of the present method
is that the oxide mixture so produced has been found to have high
surface area and high oxygen storage capacities at lower
temperatures while consuming lower contents of metals such as
palladium. As described below the presence of zirconium with the
praseodymium increases surface area stability of the oxide mixture.
Such advantage provides for significant cost savings in
manufacturing exhaust gas catalyst capable of lowering cold-start
emissions through an exhaust stable catalyst, such as a three-way
catalyst. The resultant praseodymium-cerium oxide mixture requires
less metals to be added thereto in order to accelerate light-off of
the catalyst. Thus, total consumption of palladium, platinum or
rhodium will be reduced with implementation of the present
invention method.
[0023] According to the present invention an oxide mixture is
provided having preferably substantially equal molar content of
praseodymium and cerium. Alternatively, the oxide mixture may be of
different molar contents of praseodymium and cerium, e.g., about
40%/60%, 60%/40%, respectively. The oxide mixture may be prepared
by any suitable means. Preferably, the oxide mixture is prepared as
described in U.S. patent application Ser. No. 08/966,729, entitled
Thermally Stable, High-Surface-Area Metal Oxides Made By Organic
Templating, which is hereby incorporated by reference. However
other suitable ways of preparing the oxide mixture may be used,
such as sol gel methods or precipitation methods do not fall beyond
the scope and spirit of this invention.
[0024] The oxide mixture is then doped with zirconium, yttrium, or
both to enhance the thermal stability of the high surface area
oxide mixture.
[0025] Generally, between 0 to about 10 weight % zirconium and
between 0 to about 10 weight % yttrium may be doped to the oxide
mixture. As described below, it has been found that higher doses of
zirconium may reduce the oxygen storage capacities of the oxide
mixture. It is preferred that the least amount of zirconium be
doped to the oxide mixture that achieves the desired
characteristics.
[0026] In a preferred embodiment, 0-2 weight % zirconium and/or
yttrium is doped to the oxide mixture. More specifically, it has
been found that the addition of zirconia tends to promote an
undesirable transformation of tetravalent praseodymia (Pr+4) to
trivalent praseodymia (Pr+3) in the praseodymia-ceria mixed oxide.
This was confirmed by thermal gravimetric analysis which showed
that the amount of oxygen reversibility released upon heating from
200.degree. to 800.degree. celsius in air decreases with increasing
levels of zirconia. Thus, only small portions of zirconium are
preferably added in order to enhance stability of the surface area
of the mixed oxides.
[0027] As shown in FIG. 1, oxide mixtures having substantially
equal molar content of praseodymium and cerium increase in surface
area as the levels of zirconium are increased in the mixtures
thereof. Moreover, FIG. 1 shows that increased contents of
zirconium in oxide mixtures having equal molar contents of
praseodymium and cerium increase the surface area of the resulting
oxide mixture for fresh or air aged oxide mixtures. The increase in
surface area of the oxide mixtures with respect to zirconium
illustrates their enhanced ability as catalyst support.
[0028] As shown in FIG. 2, increased levels of zirconium in oxide
mixtures having equal molar content of praseodymium and cerium
result in a decrease of the oxygen storage capacities of the
resulting oxide mixtures. Moreover, FIG. 2 shows that as levels of
zirconium increase in oxide mixtures, oxygen storage capacities of
such oxide mixtures also decrease consistent with temperature. The
decrease of oxygen storage capacities of the oxide mixtures
illustrates an adverse effect of zirconium on catalyst support.
Additionally, FIGS. 1 and 2 together illustrate the need to
optimize the amounts of zirconium doped to the oxide mixture.
[0029] As shown in FIG. 3, resulting oxide mixtures having
praseodymium at 100.degree. to 250.degree. celsius have typically
higher oxygen storage capacities than the resulting oxide mixture
without praseodymium contents. Additionally, FIG. 3 also shows that
oxide mixtures having greater contents of zirconium typically have
a lower oxygen storage capacity than oxide mixtures having less
zirconium contents.
[0030] Doping of the oxide mixture with zirconium, yttrium, or both
may be achieved according to the preparation of preparing oxide
mixtures as described in U.S. patent application Ser. No.
08/966,729 entitled Thermally Stable, High-Surface-Area Metal
Oxides Made By Organic Templating which has been hereby
incorporated by reference.
[0031] After the oxide mixture is doped, precious metal is added to
the oxide mixture. Generally, 0-2 weight % precious metal is added
to the oxide mixture. Specifically, the precious metals which may
be added include palladium, platinum or rhodium. Preferably, 0.1 to
1.5 weight % of metal may be added to the oxide mixture. Moreover,
a combination of the three precious metals may be added at any
suitable ratios. Addition of the precious metal may be performed by
impregnating the oxide mixture therewith, as known in the art.
[0032] It has been found that if precious metal is added to the
mixed oxide at the time the mixed oxide is made, then oxygen
storage capacities and surface areas of the mixed oxides are
typically higher than when precious metal is added at a time after
the oxide is made. Thus, it is preferred that the precious metal be
added to the oxide mixture at the time the oxide mixture is
prepared and doped. However, it is to be noted that adding precious
metal at a later time does not fall beyond the scope and spirit of
this invention.
[0033] FIG. 4 illustrates that by providing an oxide mixture having
praseodymium and by adding precious metals to the mixed oxide at
the time the oxide mixture is made, a catalyst with higher oxygen
storage capacity at low temperatures is obtained. As shown in FIG.
4, a catalyst having praseodymium has a higher oxygen storage
capacity than catalysts without praseodymium. In turn, less
precious metals, such as palladium, are required to obtain a given
oxygen storage capacity. A decrease in content of palladium per
unit weight of catalyst results in a substantial cost savings in
manufacturing exhaust gas catalysts.
[0034] After the precious metal is added, gamma alumina is mixed
with the oxide mixture for washcoating. Gamma alumina aids in
bonding the contents to achieve a monolithic catalyst having
increased oxygen storage capacities. Gamma alumina may be mixed
with the oxide mixture at about 0.1/1 to 1/1 in gamma alumina/oxide
mixture molar ratios.
[0035] As known, there are a number of ways to mix gamma alumina
with the oxide mixture for washcoating. All of such known methods
may be used in this invention for such purpose and do not fall
beyond the scope and spirit of this invention.
[0036] The resulting oxide mixture may then be washcoated onto a
monolithic substrate. As known, there are a number of ways to
washcoat the mixture onto the monolithic substrate. Any such
methods may be used for this purpose and do not fall beyond the
scope and spirit of this invention. Among the list of known
methods, there is included dipping the washcoat into a slurry
containing the oxide mixture, and blowing the resulting oxide
mixture onto the washcoat, etc.
[0037] The substrate typically may be a substrate including
cordierite substrate or metallic substrate. The additional weight
of the resulting oxide mixture to be washcoated onto the substrate
is about 30%-50% of the weight of the initial substrate.
EXAMPLE 1
[0038] Praseodymium-cerium oxide mixture is prepared at equally
molar contents, specifically 45 weight percent each. Ten weight
percent zirconium is doped to the oxide mixture and 2 weight
percent palladium was added thereafter. Gamma alumina is then mixed
to the oxide mixture for washcoating and the oxide mixture is then
washcoated onto a monolithic substrate, specifically cordierite
substrate.
EXAMPLE 2
[0039] Praseodymium-cerium oxide mixture is prepared at equally
molar contents, specifically 42.5 weight percent each. Fifteen
weight percent zirconium was doped to the oxide mixture and 2
weight percent palladium is added thereafter. Gamma alumina is then
mixed to the oxide mixture for washcoating and the oxide mixture is
then washcoated onto a monolithic substrate, specifically
cordierite substrate.
EXAMPLE 3
[0040] Praseodymium-cerium oxide mixture is prepared at equally
molar contents, specifically 40 weight percent each. Twenty weight
percent zirconium is doped to the oxide mixture and 2 weight
percent palladium was added thereafter. Gamma alumina is then mixed
to the oxide mixture for washcoating and the oxide mixture is then
washcoated onto a monolithic substrate, specifically cordierite
substrate.
EXAMPLE 4
[0041] Praseodymium-cerium oxide mixture is prepared at equally
molar contents, specifically 31 weight percent each. Thirty-eight
weight percent zirconium is doped to the oxide mixture and 2 weight
percent palladium was added thereafter. Gamma alumina is then mixed
to the oxide mixture for washcoating and the oxide mixture is then
washcoated onto a monolithic substrate, specifically cordierite
substrate.
[0042] While embodiments of the invention have been illustrated and
described, it is not intended that these embodiments illustrate and
describe all possible forms of the invention. Rather, the words
used in the specification are words of description rather than
limitation, and it is understood that various changes may be made
without departing from the spirit and scope of the invention.
* * * * *