The enhanced deNO(x) performance of the Ag/Al2O3 catalyst by addition of H-2 was investigated for HC-SCR using a mixture of simulated diesel and ethanol as the reductant. As H-2 concentration increased in the feed-gas stream, the low-temperature NOx reduction activity was remarkably enhanced. Addition of H-2 promoted the oxidation of both NO and hydrocarbons, resulting in an increased formation of nitrates, enolic, and isocyanate species regarded as reaction intermediates. Results of the UV-vis indicated that H-2 promoted the transformation of Ag+ to Ag-n(delta+) and Ag-0 on the surface of Ag/Al2O3 catalyst, while those of H-2-TPR, O-2-TPD, in situ FTIR, and TGA revealed the formation of highly mobile and reactive oxygen species under the (O-2 + H-2) flow. A reaction mechanism is proposed to elucidate the role of H-2 in the enhancement of deNO(x) performance of HC-SCR in view of morphological, chemical, and kinetic changes of the Ag/Al2O3 catalytic system. (C) 2013 Elsevier Inc. All rights reserved.