Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Mixture is exhaust from internal-combustion engine
Reexamination Certificate
1999-10-22
2001-07-03
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Mixture is exhaust from internal-combustion engine
C423S213200, C423S213700, C060S299000, C060S302000
Reexamination Certificate
active
06254842
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an article and method comprising a catalyst composition useful for the treatment of gases to reduce pollutants contained therein. More specifically, the present invention is concerned with catalysts of the type generally referred to as “close coupled catalysts” which are designed to reduce pollutants in engine exhaust emissions during engine cold start conditions.
2. Description of the Related Art
California Low Emission Vehicle standards require significantly higher emissions reduction, especially for hydrocarbon and nitrogen oxides. For a typical vehicle, a large portion (up to 80%) of the hydrocarbon emissions occurs during the first phase of the Federal Test Procedure (“FTP”). A variety of technologies are under development to reduce cold start hydrocarbon emissions, including close coupled catalysts as disclosed in Ball, D. J., “Distribution of Warm-Up and Underfloor Catalyst Volumes”, SAE 922338, 1992; electrically heated catalysts as disclosed in Piotrowski, G. K., “Evaluation of a Resistively Heated Metal Monolith Catalytic Converter on a Gasoline-Fueled Vehicle”, EPA/AA/CTAAB/88-12, 1988 and Hurley, R. G. “Evaluation of Metallic and Electrically Heated Metallic Catalysts on a Gasoline Fueled Vehicle”, SAE 900504, 1990; hydrocarbon absorbers as disclosed in Heimrich, M. J., Smith, L. R., and Kitowski, J., “Cold Start Hydrocarbon Collection for Advanced Exhaust Emission Control, SAE 920847, 1992 and Hochmuth, J. K., Burk, P. L., Telentino, C., and Mignano, M. J., “Hydrocarbon Traps for Controlling Cold Start Emissions”, SAE 930739, 1993; by-pass catalysts as disclosed in Fraidl, G. K., Quissrk, F. and Winklhofer, E., “Improvement of LEV/ULEV Potential of Fuel Efficient High Performance Engines,” SAE 920416, 1992; and burners as disclosed in Ma, T., Collings, N. and Hands, T., “Exhaust Gas Ignition (EGI)—A New Concept for Rapid Light-off of Automotive Exhaust Catalyst, SAE 920400, 1992. It has been reported that close coupled catalysts, especially Pd-containing catalysts, are very effective at reducing HC emission during cold start of the FTP cycle as disclosed in Ball, D. J., “Distribution of Warm-Up and Underfloor Catalyst Volumes”, SAE 922338, 1992; Summers, J. C., Skowron, J. F., and Miller, M. J., “Use of Light-Off Catalysts to Meet the California LEV/ULEV Standards”, SAE 930386, 1993 and Ball, D. J., “A Warm-up and Underfloor Converter Parametric Study”, SAE 932765, 1993. Recently, Ford has reported a successful application of Pd-only catalyst for meeting stringent emission standards as disclosed in Dettling, J., Hu, Z, Lui, Y., Smaling, R., Wan, C and Punke, A., “SMART Pd TWC Technology to Meet Stringent Standards”, Presented at CAPoC
3
Third International Congress on Catalyst and Automobile Pollution Control, Apr. 20-22, 1994, Brussels.
The principal function of a close coupled catalyst, also referred to as “precat” and “warm-up” catalysts, is to reduce hydrocarbon emissions during cold start. Cold start is the period immediately after starting the engine from ambient conditions. The cold start period depends on the ambient temperature, the type of engine, the engine control system and engine operation. Typically, the cold start period is within the first two minutes after the start of an engine at ambient temperature, FTP Test 1975 characterize cold start as the first bag of the FTP driving cycle which lasts for the first 505 seconds after starting an engine from ambient temperature, typically at 26° C. This is accomplished by locating at least part of the total exhaust system catalyst closer to the engine than traditional “underfloor catalyst”. The underfloor catalyst are typically located beneath the floor of the vehicle. The close coupled catalyst is located in the engine compartment, i.e., beneath the hood and adjacent to the exhaust manifold. There are two possible strategies for implementing a close coupled catalyst. The close coupled catalyst can occupy the entire catalyst volume or be a small volume catalyst used in conjunction with an underfloor catalyst. The design option depends on the engine configuration, size and space available.
Catalysts at the close coupled position are also exposed to high temperature exhaust gas immediately exiting the engine after the engine has warmed up. As a consequence, the close coupled catalyst must have high temperature stability to be durable enough for meeting stringent emission standards as disclosed in Bhasin, M. et al, “Novel Catalyst for Treating Exhaust Gases from Internal Combustion and Stationary Source Engines”, SAE 93054, 1993. In the present day vehicle control strategies, overfueling or fuel enrichment is used to cool the engine exhaust prior to the catalyst during high load operation or high exhaust temperature conditions. This strategy results in increased hydrocarbon emissions and may be eliminated in future regulations as disclosed in “Acceleration Enrichment May Be Large Source of Pollution”, WARD'S Engine and Vehicle Technology Update, Dec. 1, 1993, p.4. This could result in 50 to 100° higher exposure temperatures for the catalyst. Thus, the close coupled catalyst could be exposed to temperatures as high as 1050° C. Additionally, high speed Autobahn driving conditions can expose the close coupled catalyst to such high temperatures.
A typical motor vehicle catalyst is an underfloor three-way conversion catalysts (“TWC”) which catalyzes the oxidation by oxygen in the exhaust gas of the unburned hydrocarbons and carbon monoxide and the reduction of nitrogen oxides to nitrogen. TWC catalysts which exhibit good activity and long life comprise one or more platinum group metals (e.g., platinum or palladium, rhodium, ruthenium and iridium) located upon a high surface area, refractory oxide support, e.g., a high surface area alumina coating. The support is carried on a suitable carrier or substrate such as a monolithic carrier comprising a refractory ceramic or metal honeycomb structure, or refractory particles such as spheres or short, extruded segments of a suitable refractory material.
U.S. Pat. No. 4,134,860 relates to the manufacture of catalyst structures. The catalyst composition can contain platinum group metals, base metals, rare earth metals and refractory, such as alumina support. The composition can be deposited on a relatively inert carrier such as a honeycomb.
The high surface area alumina support materials, also referred to as “gamma alumina” or “activated alumina”, typically exhibit a BET surface area in excess of 60 square meters per gram (“m
2
/g”), often up to about 200 m
2
/g or more. Such activated alumina is usually a mixture of the gamma and delta phases of alumina, but may also contain substantial amounts of eta, kappa and theta alumina phases. It is disclosed to utilize refractory metal oxides other than activated alumina as a support for at least some of the catalytic components in a given catalyst. For example, bulk ceria, zirconia, alpha alumina and other materials are known for such use. Although many of these materials suffer from the disadvantage of having a considerably lower BET surface area than activated alumina, that disadvantage tends to be offset by a greater durability of the resulting catalyst.
In a moving vehicle, exhaust gas temperatures can reach 1000° C., and such elevated temperatures cause the activated alumina (or other) support material to undergo thermal degradation caused by a phase transition with accompanying volume shrinkage, especially in the presence of steam, whereby the catalytic metal becomes occluded in the shrunken support medium with a loss of exposed catalyst surface area and a corresponding decrease in catalytic activity. It is a known expedient in the art to stabilize alumina supports against such thermal degradation by the use of materials such as zirconia, titania, alkaline earth metal oxides such as baria, calcia or strontia or rare earth metal oxides, such as ceria, lanthana and mixtures of two or more rare earth metal oxides. For example, see C. D.
Heck Ronald M.
Hu Zhicheng
Rabinowitz Harold N.
Engelhard Corporation
Griffin Steven P.
Negin Richard A.
Strickland Jonas N.
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