Patent ID: 6161378
Filing Date: 2000-12-19
Classification: B01D,F01N,F02D,Y02A,Y02T

Abstract:
A method of purifying an exhaust gas from an internal combustion engine having a lean operation mode, comprising:providing a catalyst which both chemically adsorbs NO.sub.x and reduces adsorbed NO.sub.x when an amount of a gaseous reducing agent in said exhaust gas is less than stoichiometric with respect to an amount of a gaseous oxidizing agent in the exhaust gas, and which catalyzes a reduction of adsorbed NO.sub.x when the amount of said reducing agent is equal to or more than stoichiometric with respect to the amount of said oxidizing agent in the exhaust gas;passing said exhaust gas over said catalyst;operating said engine in said lean combustion mode; andintermittently controlling said amount of said reducing agent present in said exhaust gas to increase it to an amount which is greater than or equal to stoichiometric with respect to an amount of said oxidizing agent in said exhaust gas;wherein said catalyst comprises at least one member selected from each of the following groups;a first group consisting of alkali metals, calcium and strontium;a second group consisting of rare earth metals;a third group consisting of platinum group metals; anda fourth group consisting of silicon and titanium.