Selective catalytic reduction of NOx by H-2 (H-2-SCR) was investigated in feed gas mixture of 1000 ppm NOx, 5000 ppm H-2, 0-20% O-2 in N-2 with GHSV of 32,000 h(-1) over Pt/HY catalyst. It was found that the N-2 selectivity exhibits a "volcano" shape versus the concentration of O-2 and NO2, and the change pattern of N-2 selectivity were determined by both of them. It is suggested that the nitrous species at the Pt-support interface being taken part in the reaction in scale is determined by the amount of H(ad) migrated there by spillover, and the reduction of them mainly produces N2O. The suggestion is strongly supported by FTIR and the relationship that more nitrous species reduction at the Pt-support interface led to lower N-2 selectivity in the H-2-SCR, respectively. It is proposed that when the amount of H(ad) is insufficient for reducing the nitrous species to N-2 on Pt surface, increasing O-2 and NO2 in the feed gas must lead to the H(ad) further decreasing, and hence cause more N2O formation there. On the other hand, the H spillover due to overmany H(ad) on Pt surface must be suppressed by increasing O-2 and NO2. (C) 2014 Elsevier B.V. All rights reserved.