The reduction of NO with H-2 in the presence of O-2 at 100-150 ° C over physical mixtures of Pt/ZrO2 and secondary catalysts active for the selective catalytic reduction of NOx with NH3 (NH3-SCR) was investigated. For high N-2 selectivity, Pt/ZrO2 particles must be in close contact with the particles of the NH3-SCR catalyst. The optimal Pt loading and calcination temperature for Pt/ZrO2 were 1 wt % and 600 ° C, respectively. H-form zeolites exhibited higher N-2 selectivity than V/TiO2. Both H-ZSM-5 and H-mordenite were favorable as NH3-SCR catalysts. The activity of a physical mixture of Pt/ZrO2 and H-ZSM-5 was not strongly influenced by changes in the O-2 or H-2 concentration or by the addition of H2O to the feed gas. The addition of CO severely suppressed the reaction owing to its strong adsorption on Pt/ZrO2. Although the addition of C3H8, C3H6, CO2, or SO2 negatively affected the activity of Pt/ZrO2 for NH3 production, the physical mixture with H-ZSM-5 maintained high NO, conversion, and only a small decrease in the N-2 selectivity was observed upon the addition of C3H6 or SO2.