Patent ID: 7490464

Claim:
A method for converting NOx in an exhaust gas from a diesel engine or lean burn gasoline engine to N 2 , comprising: (a) contacting the exhaust gas comprising NOx in a lean period with a NOx storage reduction (NSR) catalyst comprising a platinum group metal component and at least 0.1 g/in 3 of a NOx sorbent, selected from the group consisting essentially of alkali and alkaline earth metal oxides dispersed on a refractory metal oxide to sorb a portion of NOx in the form of alkaline earth metal nitrate from the exhaust gas and allowing a portion of the NOx to flow through the NSR catalyst untreated; (b) periodically altering the air/fuel ratio of the exhaust stream to provide a rich gaseous stream during a rich period; (c) contacting the rich gaseous stream with the NSR catalyst to reduce the sorbed NOx to NH 3 ; and, (d) subsequently contacting a mixture of the NH 3 and the untreated NOx in the exhaust gas with an SCR catalyst to form N 2 , wherein the NSR further comprises an oxygen storage component selected from one or more oxides of cerium and praseodymium in an amount less than 0.5 g/in 3 .