CATALYST FOR PURIFICATION OF LEAN EXHAUST GAS

摘要

PROBLEM TO BE SOLVED: To suppress sulfur poisoning of a ceria-zirconia solid soln. in a lean exhaust gas and to improve the durability of the catalyst. SOLUTION: This catalyst consists of an oxide solid soln., a refractory porous body and catalytic noble metals deposited on these. The oxide solid soln. contains a ceria-zirconia solid soln. having >=50% solubility of zirconia in ceria and having <=10 nm average grain size, and the molar ratio of zirconium in the ceria-zirconia solid soln. ranges 0.55<=Zr/(Ce+Zr)<=0.90. Moreover, the oxide solid soln. contains oxides of rare earth elements M excluding cerium by the molar ratio to the ceria-zirconia solid soln. ranging 0.03<=M/(Ce+Zr+M)<=0.1. Since the amt. of cerium which easily produces sulfates is relatively small and the solid soln. phase is thermodynamically stable to hardly produce sulfates, the obtd. catalyst prevents sulfur poisoning.