The effect of H-2 addition on the selective catalytic reduction of NOx with propene (C3H6-SCR of NOx) has been investigated using a metal-monolithic anodic alumina-supported Ag catalyst. The low temperature de-NOx activity of the Ag/Al2O3 catalyst is markedly enhanced by the addition of a small amount of H-2, which is associated with the improved propene activation at low temperatures. The addition of H-2 greatly promotes the nitrate de-composition at low temperatures, which is believed to alleviate nitrate poisoning and initiate the SCR reaction at low temperatures, because of the formation of free silver sites. Furthermore, it is suggested that a small amount of H-2 addition will further reduce the freed Ag+ species into Ag-n(delta+) and eventually lead to the improved de-NOx activity, because Ag-n(delta+) is more active in propene activation than Ag+ at low temperatures. However, excess H-2 and high Ag loading mainly promoted the nonselective combustion of propene with oxygen, rather than the selective oxidation of propene with NOx.