EXHAUST GAS PURIFYING CATALYST

摘要

An exhaust gas purifying catalyst comprising a base material, a coat layer formed on the base layer and consisting of a porous carrier, and noble metal carried on the coat layer, wherein the coat layer is such that the pore volume of pores 0.1-20 mu m in diameter accounts for at least 50 % of that of pores up to 50 mu m in diameter, and the pore volume of pores 0.5-10 mu m in diameter accounts for at least 20 % of that of pores up to 50 mu m. In comparison with conventional coat layers where pores 0.01 mu m in diameter account for the majority of the pores, a pore diameter is 10- to 2000-folded, and a gas diffusion speed through pores is also 10- to 2000-folded. In addition, noble metal carried up to the inside of a coat layer and along pores can restrict the grain growth of noble metal and increase a utilization efficiency of an NOx occluding agent within the coat layer. Accordingly, an increase in NOx occluding amount in a lean oxygen surplus atmosphere is made compatible with a high-efficiency occluded NOx reduction/purification by a short-time rich spike.