Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
2001-12-10
2004-09-28
Nguyen, Cam N. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S302000, C502S327000, C502S328000, C502S332000, C502S333000, C502S334000, C502S336000, C502S338000, C502S339000, C502S349000, C502S439000
Reexamination Certificate
active
06797668
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a catalyst for purifying exhaust gases from internal combustion engines. More specifically, it relates to a catalyst for purifying exhaust gases with a high efficiency under not only small but also large fluctuation conditions of air to fuel ratio (A/F).
2. Description of Related Art
Catalysts, which are placed in an exhaust gas pipe of automobiles, have been used for purifying exhaust gases since the enactment of Musky law. For gasoline engines so called Three Way Catalyst is standardized in which techniques have been proposed for simultaneously removing hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) using the catalytic composite of noble metals such as platinum, rhodium and palladium, and functional materials of ceria or the like. In the recent years, it is a growing demand for catalysts to have much catalytic efficiency and multiple functions for the treatment of exhaust gases on account of the social attention for clean air or the reinforcement of legal controls for automotive emissions.
The followings are the examples of potential demand for Three way (type) catalyst for the treatment of exhaust gas. 1. The treatment of unburned HC generated at cold-start operation. (A catalyst usually does not work efficiently at cold temperature) 2. Durability improvement 3. The response of catalyst for the various driving conditions, especially in acceleration/deceleration driving, which can induce large fluctuations of A/F and space velocity (SV), then cause the change of catalyst efficiency. To control emissions, therefore, automotive manufactures pay much effort on the control of (A/F) in various driving conditions, e.g., by adjusting (A/F) to near stoichiometry region using sensors and modeling method, as the performance of catalyst could change drastically with the change of (A/F).
Ceria has a function of storing and emitting oxygen according to the change of atmospheres (hereinafter it may be referred to as OSC: Oxygen Storage Component), which can improve the function of catalysts. However, since ceria itself has poor heat-resistance, OSC materials with a high heat-resistance have been developed by combining cerium with other elements such as zirconium. JP-A-10-182,155 discloses cerium-zirconium complex oxides and the catalyst containing the oxide of the solid solution uniformly prepared has a superior catalyst activity. JP-A-10-194,742 and Japanese Patent No.2,787,540 proposed preparations for solid solution oxides.
However, conventional oxygen storage materials have drawbacks that they act effectively for small fluctuations nearby the stoichiometric A/F but do not act fully under relatively large fluctuations conditions.
SUMMARY OF THE INVENTION
In view of the above affairs, an object of the present invention is to provide a catalyst for purifying exhaust gases with a high efficiency under conditions of large fluctuations of A/F, and a production method thereof.
According to the present invention, there is provided an improved exhaust gas purifying catalyst comprising a complex of the oxides of cerium and a solid solution oxide containing Zr and Ce.
According to the present invention, there is provided a method for producing exhaust gases purification catalyst, comprising depositing a soluble salt of cerium to a solid solution oxide containing Zr and Ce to form a complex thereof.
The technical scope of the present invention extends to the extent that is readily replaced with persons skilled in the art without being limited by the words or terms defined in the claims of the present invention.
According to the present catalyst, it can efficiently remove CO, HC, and NOx from exhaust gases of internal combustion engines such as gasoline engines as a type of Three Way Catalyst, even under conditions of large fluctuations of A/F by not reducing much of its efficiency, especially for CO/NOx, and maintain its activities with practical durability.
The above and other objects, features and advantages of the present invention will become clear from the following description of the preferred embodiments.
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Fish & RIchardson P.C.
ICT Co., Ltd.
Nguyen Cam N.
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