Abstract: The effect of H2 on the selective catalytic reduction (SCR) of NOx by C3H6 was investigated over Ag/Al2O3 and Cu/Al2O3 catalysts by steady in situ diffuse reflectance infrared Fourier transform spectroscopy. The presence of H2 might accelerate the partial oxidation of C3H6 over Ag/Al2O3 to enolic species and acetate. The enolic species can react easily with nitrates to form surface -[KG-20x]NCO species. An enhancement of enolic species formation promoted the SCR of NOx over Ag/Al2O3 in the presence of H2. As for the Cu/Al2O3 catalyst, the addition of H2 did not influence the partial oxidation of C3H6 to acetate but inhibited apparently the formation of nitrates, and subsequently blocked the reaction between acetate and nitrates to form the key -[KG-20x]NCO species. This led to the deactivation of Cu/Al2O3 in the SCR of NOx in the presence of H2.

Key words: hydrogen, silver, copper, alumina, nitrogen oxide, selective catalytic reduction, in situ diffuse reflectance infrared Fourier transform spectroscopy, enolic species, isocyanate species