CATALYST FOR PURIFYING EXHAUST GAS AND METHOD THEREFOR

摘要

PURPOSE:To remove HC with high efficiency by introducing secondary air at the start of an engine when a large amt. of HC is generated by incorporating at least Pt or Pd into the uppermost surface of the upstream catalyst bed as a catalytically active component and at least Rh into the downstream catalyst bed. CONSTITUTION:The upstream side of a monolithic carrier 14 is coated with the upstream catalyst bed having hydrocarbon purifying activity and contg. at least Pt or Pd in the uppermost surface layer as a catalytically active component, and the downstream side is coated with a downstream catalyst bed having a ternary performance and contg. at least Rh as the catalytically active component. Consequently, secondary air is introduced to form a fuel-lean side to efficiently remove HC at the start of an engine when a large amt. of HC is generated, and the gas warming characteristic is improved by the heat of reaction generated at this time. Further, the ternary performance is appropriately exhibited even in the steady operation after the gas is warmed.