An exhaust gas after treatment system for an engine comprises an oxidation catalyst NOx adsorber wherein an oxidation catalyst compound and a NOx adsorber compound are disposed. A fuel injector is connected to and is in fluid communication with the oxidation catalyst NOx adsorber device for delivery of a hydrocarbon fuel thereto and an air pump is connected to and is in fluid communication with the oxidation catalyst NOx adsorber device for delivery of air thereto. The fuel injector and the air pump supply fuel and air to the oxidation catalyst NOx adsorber device for oxidation thereof and heating of the NOx adsorber compound to a NOx release temperature following shut down of the internal combustion engine.