Abstract: A method is provided for regenerating a LNT in a diesel engine exhaust aftertreatment system. Typically, the aftertreatment system comprises a fuel reformer, a LNT, and a SCR catalyst in that order. Over the course of the regeneration, the concentration or flow rate of syn gas is increased, peaked, and then reduced. Preferably, the syn gas concentration or flow rate and the fuel reformer temperature are simultaneously controlled using at least a fuel injector and an engine intake air throttle. The pattern of increasing the syn gas concentration or flow rate during a first part of the regeneration and decreasing the syn gas concentration of flow rate in a latter part of the regeneration reduces the fuel penalty for the regeneration and improves the ammonia production rate as compared to a system in which the syn gas concentration or flow rate is essentially constant throughout the regeneration.