Patent ID: 8240132

Claim:
A method of controlling NO x and NH 3 emissions from an exhaust stream of a diesel engine, comprising: providing a lean NO x trap, having a rich and lean cycle, in communication with the diesel exhaust stream; operating the lean NO x trap at a temperature of 150°-300° C. and elongating the rich cycle, wherein the lean NO x trap, produces and releases an optimum amount of NH 3 to provide a NO x reduced diesel exhaust stream including NO x and an optimum amount of NH 3 ; providing an NH 3 -SCR catalyst, which does not require injection of a reducing agent, in communication with the NO x reduced diesel exhaust stream, for adsorbing NH 3 , wherein the NH 3 adsorbed by the NH 3 -SCR catalyst reacts with NO x in the NO x reduced diesel exhaust stream to improve the reduction of NO x and NH 3 ; and wherein when the engine is run rich sufficient reductants and an optimum amount of NH 3 are generated in situ over the lean NO x trap, to force the reaction between NO x and NH 3 , such that NH 3 emissions are controlled and net NO x conversion maximized by the NH 3 -SCR catalyst operating in conjunction with the lean NO x trap.