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/ZrP 2 O 7 catalysts exhibiting high activity for catalytic NO x reduction by H 2 in the presence of excess O 2 were developed in this study. At a low temperature of 125 °C and a high space velocity of approximately 5 × 10 4 h –1, 0.4 wt % Pt/ZrP 2 O 7 facilitated a higher NO conversion to N 2 (51%) than 0.4 wt % Pt/ZrO 2 (<5%) for a reaction mixture of 200 ppm NO, 5000 ppm H 2, 10% O 2, and He balance. However, N 2 O and NO 2 production increased at temperatures lower than 100 °C and higher than 200 °C, thereby decreasing the N 2 yield. High-resolution electron microscopy and X-ray photoelectron spectroscopy analyses of 0.4 wt % Pt/ZrP 2 O 7 revealed the coexistence of large metallic Pt crystallites with sizes of ∼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 ZrP 2 O 7 . Owing to this structural change, N 2 O/NO 2 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 (NH 3, N 2 O, and NO 2 ) at 175 °C. The Pt oxide nanocluster supported on ZrP 2 O 7 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.