CATALYST FOR CLEANING LEAN EXHAUST GAS

摘要

PROBLEM TO BE SOLVED: To provide a catalyst for cleaning lean exhaust gas by which ceria/ zirconia solid solution in lean exhaust gas is inhibited from being poisoned by sulfur and durability is enhanced. SOLUTION: The catalyst for cleaning lean exhaust gas is constituted of oxide solid solution particles, in which solid solubility of zirconium oxide for cerium oxide in ceria/zirconia solid solution is >=50% and average diameter of crystallite is <=10 nm and furthermore ratio of zirconium is a range of 0.55<=Zr/(Ce+Zr)<=0.90 as mole ratio, of catalytic noble metal and a fire resistant porous body. Poisoning caused by sulfur is prevented because the amount of cerium easily forming sulfate is relatively little and solid solution phase is thermodynamically stabilized and sulfate is made difficult to be produced.