Complex oxide, method for producing same, and exhaust gas purifying catalyst

Abstract

Disclosed are a composite oxide which is capable of maintaining a large volume of pores even used in a high temperature environment, and which has excellent heat resistance and catalytic activity, as well as a method for producing the composite oxide and a catalyst for exhaust gas purification employing the composite oxide. The composite oxide contains cerium and at least one element selected from aluminum, silicon, or rare earth metals other than cerium and including yttrium, at a mass ratio of 85:15 to 99:1 in terms oxides, and has a property of exhibiting a not less than 0.30 cm3 / g, preferably not less than 0.40 cm3 / g volume of pores with a diameter of not larger than 200 nm, after calcination at 900° C. for 5 hours, and is suitable for a co-catalyst in a catalyst for vehicle exhaust gas purification.

Description

FIELD OF ART[0001]The present invention relates to a composite oxide which may be used as a catalyst, functional ceramics, solid electrolyte for fuel cells, abrasive, and the like, particularly suitably used as a co-catalyst material in catalysts for purifying vehicle exhaust gas and the like, and which has a large pore volume, causing excellent catalytic performance, as well as to a method for producing the composite oxide and a catalyst for exhaust gas purification employing the composite oxide.BACKGROUND ART[0002]Catalysts for purifying vehicle exhaust gas and the like are composed of a catalytic metal such as platinum, palladium, or rhodium, and a co-catalyst for enhancing the catalyst action of such metal, both supported on a catalyst support made of, for example, alumina or cordierite. The co-catalyst material absorbs oxygen under the oxidizing atmosphere and desorbs oxygen under the reducing atmosphere, and functions to optimally maintain the air / fuel ratio so that the cataly...

AI Technical Summary

Benefits of technology

[0011]It is an object of the present invention to provide a composite oxide which is capable of maintaining a large pore volume even in use in a high temperature environment, which brings about excellent heat resistance and catalytic activity, and which is particularly suitable for a co-catalyst for a catalyst for exhaust gas purification, as well as a catalyst for exhaust gas purification utilizing the composite oxide.

[0012]It is another object of the present invention to provide a method for producing a composite oxide which realizes easy production of the composite oxide of the present invention capable of maintaining a large pore volume even in use in a high temperature environment.

[0023]The composite oxide according to the present invention contains at least one element selected from aluminum, silicon, or rare earth metals other than cerium and including yttrium (sometimes referred to as the particular rare earth metals hereinbelow) at the particular ratio, and is capable of maintaining a large pore volume even in use in a high temperature environment. Thus the composite oxide according to the present invention, when used as a co-catalyst in a catalyst for exhaust gas purification, provides particularly effective purification of exhaust gas.

[0024]The method for producing a composite oxide according to the present invention includes the steps (a) to (g), in particular, step (f) of adding a surfactant after step (e), so that the composite oxide according to the present invention may be obtained conveniently.

Problems solved by technology

This results in reduction of its pore volume, causing aggregation of the catalytic metals and decrease in the contact area between exhaust gas and the catalytic metals, which leads to reduction of efficiency in purifying exhaust gases.

Besides, the method disclosed in this publication does not provide a composite oxide having a larger volume of pores with a diameter of not larger than 200 nm after calcination at 900° C. for 5 hours, than the composite oxide taught in Patent Publication 1.