Mitsui Minings & Melting Co., Ltd.

Masatoshi Yamazaki

Isamu Yashima

Yasuhide Yamaguchi

Yuichi Anno

Kiyoshi Shinoda

A co-catalyst for purifying an exhaust gas which can be used for a loner period of time as an actual catalyst by using the cerium oxide in the conventional co-catalyst for purifying the exhaust gas as a cerium-containing complex oxide for elevating the resistance to heat and suppressing the performance reduction due to thermal deterioration and by making a specific surface area and an oxygen storage capacity over specified values. A co-catalyst for purifying an exhaust gas of the present invention includes a composite oxide including (a) cerium; and (b) at least one element selected from the group consisting of zirconium, yttrium, strontium, barium and a rare-earth element supported on a particulate aluminum oxide support; a specific surface area of the co-catalyst after sintering being not less than 40 m2/g; an oxygen storage capacity at 400&deg; C. being not less than 10 &mgr;mols/g and an oxygen storage capacity at 700&deg; C. being not less than 100 &mgr;mols/g.

Co-catalyst for purifying exhaust gas

The promoter includes (A) particulate aluminum oxide and (B) a double oxide of (i) cerium and (ii) at least one member selected from the group consisting of zirconium, yttrium, strontium, barium and rare earth elements, supported on the particulate aluminum oxide. A solution of (i) a water-soluble salt of cerium and (ii) a water-soluble salt of at least one member selected from the group consisting of zirconium, yttrium, strontium, barium and rare earth elements is formed. Particulate aluminum oxide is added to the solution to form a dispersion. An aqueous solution of ammonium hydrogen carbonate is added to the dispersion to obtain particulate aluminum oxide coated with a reaction product. The particulate aluminum oxide coated with the reaction product is fired. Alternatively, an aqueous solution containing (i) the water-soluble salt of cerium and (ii) the water-soluble salt of the at least one member dissolved therein is adhered onto particulate aluminum oxide. The particulate aluminum oxide provided thereon with the aqueous solution adhered thereto is brought into contact with an aqueous solution of ammonium hydrogen carbonate to cause a reaction between these solutions and to thus deposit a reaction product on the particulate aluminum oxide. The particulate aluminum oxide with the reaction product deposit is fired.

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Saitama, Japan

Masatoshi Yamazaki