Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Mixture is exhaust from internal-combustion engine
Reexamination Certificate
1999-05-21
2001-05-22
Dunn, Tom (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Mixture is exhaust from internal-combustion engine
C423S212000, C423S213200, C423S239100, C423S239200
Reexamination Certificate
active
06235255
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to catalyst support that, when combined with noble metal to form a catalyst, exhibits superior fresh and aged performance when used to treat exhaust gas from internal combustion engines operating with an amount of air in excess of that required to combust the fuel supplied, i.e., “lean-burn” engines. More particularly, the present invention relates to a catalyst support comprising an inorganic oxide and zeolite in the proton form and having a high Si/Al ratio, wherein the zeolite is selected from those protonated zeolites that would exhibit a high Na/Al mole ratio if treated with a non-basic solution of a sodium salt until all sites that will accept a sodium ion have done so. This invention also relates to catalysts that are made from such support, to a method of treating exhaust gas from “lean-burn” engines using a catalyst of this invention, and to a method for determining if a zeolite is a suitable support component.
BACKGROUND OF THE INVENTION
Much research has been done to develop catalysts that reduce the amounts of CO, hydrocarbons and NO
x
emitted to the atmosphere in the exhaust gases of internal combustion engines. More recently, because automobile manufacturers have chosen to produce “lean-burn” engines to improve fuel economy, this research has concentrated on reducing those emissions from internal combustion engines that operate lean. Catalysts that were found to be effective in reducing emissions of CO, hydrocarbons (HC), particulate matter (PM) and NO
x
(i.e., “Four-Way Catalysts”) emitted from engines operating with a stoichiometric amount of combustion air have, in many cases, been found to be less effective in reducing NO
x
in exhaust gases from lean-burn engines, particularly after the catalysts have been used for a period of time, i.e., aged.
A good deal of the most recent research in emissions control catalysts has been focused on the control of hydrocarbon emissions during the period shortly after engine start-up, often referred to as “cold start”. For example, U.S. Pat. No. 5,284,638 (Hertl, et al.), U.S. Pat. No. 5,662,869 (Abe, et al.) and U.S. Pat. No. 5,814,287 (Adamczyk, Jr., et al.) teach the use of a hydrocarbon adsorbent along with a conventional three-way catalyst, while U.S. Pat. No. 5,772,972 (Hepburn, et al.) teaches a hydrocarbon adsorbent along with a Pd-based three-way catalyst.
Other researchers of lean-burn catalysts have focused their efforts on various metal systems on conventional supports. For example, U.S. Pat. No. 5,618,505 (Subramanian, et al.) teaches a two-stage catalyst system comprising a first stage of tungsten on &ggr;-alumina and a second stage of &ggr;-alumina with Cu, Co, Fe, or Mn dispersed thereon.
Many patents have been granted on lean-burn catalysts of various metals on zeolite supports also. For example, U.S. Pat. No. 5,270,024 (Kasahara, et al.) teaches a catalyst comprising a zeolite with a silica/alumina ratio of at least 10 with Cu and one rare earth dispersed thereon; U.S. Pat. No. 5,407,651 (Kawai) teaches a catalyst comprising a zeolite, and optionally alumina, having Mn, Co+Pd, or Co+Ag dispersed thereon; U.S. Pat. No. 5,443,803 (Mizuno, et al.) teaches a two-stage catalyst comprising zeolite with Co and an alkaline earth metal and zeolite with Cu; U.S. Pat. No. 5,409,671 (Takemoto, et al.) teaches a two-layer catalyst, the first layer being a Na-type zeolite having a silica/alumina ratio of 30 impregnated with Cu and a second layer of zeolite impregnated with Cu and Zr; and U.S. Pat. No. 5,433,933 (Eshita, et al.) teaches a zeolite having a silica/alumina ratio of at least 15 impregnated with Co and optionally an alkaline earth metal or rare earth metal.
None of these researchers have investigated the character of the zeolite used in their catalysts beyond those few who have specified a minimum silica/alumina ratio. This invention teaches that the performance, both new and when aged, of lean-burn catalysts is improved when particular zeolites are used in the support formulation.
SUMMARY OF THE INVENTION
This invention relates to catalyst support which, when combined with noble metal to form a catalyst, forms a catalyst that is superior in reducing noxious emissions from internal combustion engines. More particularly, this invention relates to catalyst supports comprising an inorganic oxide, preferably alumina, and zeolite in the proton form and having a high Si/Al ratio, wherein the zeolite is selected from those protonated zeolites that would exhibit a high Na/Al mole ratio if treated with a non-basic solution of a sodium salt until all sites that will accept a sodium ion have done so. This invention also relates to catalysts that are made from such supports, to a method of treating exhaust gas from “lean-burn” engines using a catalyst of this invention, and to a method for determining if a zeolite is a suitable support component.
The support of the present invention comprises between about 10 wt. % and about 80 wt. % an inorganic oxide, preferably alumina and most preferably &thgr;-alumina, and the balance zeolite, preferably ZSM-5. Catalyst of this invention comprises such support on which has been dispersed between about 0.0283 g/m
3
(1 g/ft
3
) and about 5.66 g/m
3
(200 g/ft
3
) of noble metal, preferably Pt.
REFERENCES:
patent: 5051244 (1991-09-01), Dunne et al.
patent: 5270024 (1993-12-01), Kasahara et al.
patent: 5284638 (1994-02-01), Hertl et al.
patent: 5407651 (1995-04-01), Kawai
patent: 5409671 (1995-04-01), Takemoto et al.
patent: 5433933 (1995-07-01), Eshita et al.
patent: 5443803 (1995-08-01), Mizuno et al.
patent: 5662869 (1997-09-01), Abe et al.
patent: 5772972 (1998-07-01), Hepburn et al.
patent: 5814287 (1998-09-01), Adamczyk, Jr. et al.
patent: 5968466 (1999-10-01), Kharas
ASEC Manufacturing
Dunn Tom
Kuffner & Associates
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