Patent ID: 6729125
Filing Date: 2004-05-04
Classification: B01D,F01N,F02D,Y02A,Y02T

Abstract:
An exhaust gas purifying system for an internal combustion engine, comprising:an exhaust gas component concentration regulating device disposed in an exhaust gas passageway of the engine, for regulating concentrations of gas components in exhaust gas discharged from the engine such that the concentrations of carbon monoxide and hydrogen are respectively not more than 2.0% by volume and not less than 0.5% by volume and such that a volume concentration ratio of [hydrogen/carbon monoxide] is not smaller than 0.5, in a first exhaust gas condition in which air/fuel ratio of exhaust gas is within a range of from a rich value to a stoichiometric value; and a NOx adsorbing and reducing catalyst disposed in the exhaust gas passageway downstream of said exhaust gas component concentration regulating device, for adsorbing nitrogen oxides in a second exhaust gas condition in which the air/fuel ratio of exhaust gas is at a lean value, and reducing the nitrogen oxides into nitrogen in the first exhaust gas condition, wherein said exhaust gas component concentration regulating device is a rich exhaust gas CO and H2 regulating catalyst for regulating a concentration of CO and H2 in rich exhaust gas which has an air/fuel ratio richer than a stoichiometric value, wherein the rich exhaust gas CO and H2 regulating catalyst is a CO decreasing catalyst for decreasing a concentration of CO in the rich exhaust gas, wherein the CO decreasing catalyst contains at least one noble metal selected from the group consisting of platinum, palladium and rhodium, and at least one selected from the group consisting of sodium, potassium, rubidium, cesium, magnesium, calcium, strontium and barium which are in a form of a compound, and wherein the CO decreasing catalyst contains at least one noble metal selected from the group consisting of platinum, palladium and rhodium in a number of moles of MP, and at least one selected from the group consisting of sodium, potassium, rubidium, cesium, magnesium, calcium, strontium and barium in a number of moles of MA, a ratio MA/MP being within a range of 0.1