Patent ID: 6397582
Filing Date: 2002-06-04
Classification: B01D,F01N,F02D,Y02A,Y02T

Abstract:
An apparatus for purifying an exhaust gas from an internal combustion engine having a lean operation mode with an air to fuel ratio of at least 18 and being shifted intermittently to a stoichiometric mode or a rich mode, said apparatus comprising:a main catalyst connected to the internal combustion engine and disposed in an exhaust gas duct to which an exhaust gas containing NOx communicates; wherein said main catalyst chemically adsorbs NOx in the exhaust gas when the internal combustion engine operates in said lean mode operation mode, retaining said NOx as NO2 on a surface portion of said main catalyst without a change of a crystallization structure of said main catalyst; and NO2 retained on said surface portion of said main catalyst is reduced to N2 in the presence of the exhaust gas, without change of the crystallization structure of said main catalyst, when the internal combustion engine is shifted to said stoichiometric mode or said rich mode and said main catalyst is regenerated.