Patent ID: 8906331

Claim:
A method of treating the exhaust gas stream flowing from a vehicle internal combustion engine during a period following a cold-start of the engine, the exhaust gas stream comprising a mixture of nitric oxide, carbon monoxide, hydrocarbons, hydrogen, water, carbon dioxide, oxygen, and nitrogen, the exhaust gas stream being at an initial temperature below 100° C. and progressively warming during further engine operation, the method comprising; continually passing the hydrogen, oxygen, and nitric oxide-containing exhaust gas stream in contact with a silver/alumina particulate catalyst to oxidize at least a portion of the nitric oxide to nitrogen dioxide and to temporarily store some of the nitrogen oxide and nitrogen dioxide product on the particulate catalyst material, the silver/alumina particulate catalyst consisting of particles of silver or silver oxide deposited on carrier particles of alumina, the silver/alumina particulate catalyst oxidizing nitric oxide to nitrogen dioxide in the presence of hydrogen and temporarily storing nitrogen oxide and nitrogen dioxide product as the exhaust gas temperature range is progressively warmed from 100° C. to 190° C.; then, continually passing the exhaust gas stream into contact with at least one downstream catalytic material for further oxidation of nitric oxide or for reduction of nitric oxide and nitrogen dioxide as the exhaust gas increases in temperature and heats each such downstream reactor to an operating temperature; and continuing the passage of the exhaust gas through each reactor during the duration of engine operation, while stored material is removed from the silver/alumina particulate catalyst and the silver/alumina particulate catalyst ceases its affect on the warmed exhaust gas stream until the engine is stopped and started again, following an engine cool-down period.