Nissan Motor Company Limited

Keiichi Sawamura

Koji Masuda

Yoshiyuki Eto

Junichi Mine

A method of producing a monolithic three-way catalyst for the purification of exhaust gases of internal combustion engines. First, a mixed oxide coating is provided to a monolithic carrier by treating the carrier with a coating slip in which an active alumina powder containing cerium in oxide form is dispersed together with a ceria powder and then baking the treated carrier. Next, Pt, Rh and/or Pd are deposited on the oxide coating by a known thermal decomposition process. The addition of the ceria powder to the coating slip is effective in enhancing the CO, HC and NO.sub.x conversions and durability of the produced catalyst at high temperatures. Preferably the content of Ce in the active alumina powder is 1-5 wt %, and, in the coating after baking, Ce of the ceria powder amounts to 5-50 wt % of the coating. Optionally a zirconia powder too may be added to the coating slip such that Zr of the zirconia powder amounts to 1-10 wt % of the coating.

Method of producing monolithic catalyst for purification of exhaust gas

A method of impregnating spheres of activated alumina with cerium in an oxidized state. The cerium-impregnated alumina spheres are for use in catalyst supports for three-way catalysts for purification of exhaust gases of automotive engines. The method has the steps of wetting spheres of activated alumina with an aqueous solution of a cerium salt, drying the wet spheres and calcining the dried spheres in an oxidizing atmosphere. The drying is performed so as to complete the removal of water from the spheres by evaporation in a time period not longer than 10 min, preferably by subjecting the wet spheres to microwave heating and most preferably by performing the microwave heating with a forced draft. By quickly completing the drying the distribution of cerium in the individual spheres becomes very uniform, and this has the effect of improving the efficiency of three-way catalysts produced by using the cerium-impregnated spheres of activated alumina.

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Yokosuka, Japan

Keiichi Sawamura