TiO 2 supported monometallic and bimetallic catalysts were prepared and employed in the selective catalytic reduction of nitrogen oxides by hydrogen (H 2 -SCR). Bimetallic Pd–Ir/TiO 2 exhibited high activity in H 2 -SCR reaction and NO x conversion of >80%, with N 2 selectivity >80%, could be obtained in the temperature range of 413–473K. The existence states of supported metals before and after H 2 -SCR were investigated by X-ray photoelectron spectroscopy, and the surface species formed during H 2 -SCR reaction were monitored by in situ FTIR spectroscopy. Based on the catalytic and characterization results, the synergistic effects between Pd and Ir were discussed and the H 2 -SCR reaction pathways over Pd–Ir/TiO 2 were proposed.