Optimization of Physical Mixtures of Pt/ZrO2 and H-Form Zeolites for Catalysis of the NO-H2-O2 Reaction

The reduction of NO with H2 in the presence of O2 at 100-150 (degree)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 N2 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 (degree)C, respectively. H-form zeolites exhibited higher N2 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 O2 or H2 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 NOx conversion, and only a small decrease in the N2 selectivity was observed upon the addition of C3H6 or SO2.