Pt Oxide Nanoclusters Supported on ZrP2O7 for Selective NO x Reduction by H2 in the Presence of O2 with Negligible NH3, N2O, and NO2 Byproducts

Pt/ZrP2O7 catalysts exhibiting high activity for catalytic NOx reduction by H-2 in the presence of excess O-2 were developed in this study. At a low temperature of 125 degrees C and a high space velocity of approximately 5 x 10(4) h(-1), 0.4 wt % Pt/ZrP2O7 facilitated a higher NO conversion to N-2 (51%) than 0.4 wt % Pt/ZrO2 (<5%) for a reaction mixture of 200 ppm NO, 5000 ppm H-2, 10% O-2, and He balance. However, N2O and NO2 production increased at temperatures lower than 100 degrees C and higher than 200 degrees C, thereby decreasing the N-2 yield. High-resolution electron microscopy and X-ray photoelectron spectroscopy analyses of 0.4 wt % Pt/ZrP2O7 revealed the coexistence of large metallic Pt crystallites with sizes of similar to 20 nm and highly dispersed Pt oxide nanoclusters. When Pt loading was decreased to 0.05 wt %, the large metallic Pt crystallites disappeared, and only the Pt oxide nanoclusters remained on ZrP2O7. Owing to this structural change, N2O/NO2 formation was significantly suppressed, enabling highly selective NO reduction to N-2. Moreover, catalyst preparation by equilibrium adsorption instead of wet impregnation further improved the reaction, achieving >90% selective NO conversion to N-2, which was nearly free of undesired byproducts (NH3, N2O, and NO2) at 175 degrees C. The Pt oxide nanocluster supported on ZrP2O7 was more tolerant to the presence of 10% water vapor in the exhaust gas than the metallic Pt particles. Therefore, the developed catalyst is suitable for applications in practical exhaust gas purification for H-2-fueled internal combustion engines.