Different Reaction Mechanisms of Ammonia Oxidation Reaction on Pt/Al₂O₃ and Pt/CeZrO₂ with Various Pt States

NH₃ emissions were limited strictly because of the threat for human health and sustainable development. Pt/Al₂O₃ and Pt/CeZrO₂ were prepared by the impregnation method. Differences in surface chemical states, reduction ability, acid properties, morphological properties, reaction mechanisms, and ammonia oxidation activity were studied. It indicated that Pt species states were affected by different metal-support interactions. The homogeneously dispersed Pt species over Pt/Al₂O₃ exposed Pt(111) because of weak metal-support interactions; there even existed an obvious interface between Pt and Al₂O₃. While obscure even an overlapped interface was observed over Pt/CeZrO₂, resulting in the formation of PtO because of the oxygen migration from CeZrO₂ to Pt species (confirmed by CO-FTIR, the cycled H₂-TPR and transmission electron microscopy results). It was noteworthy that different reaction mechanisms were induced by different states of Pt species; NH was the key intermediate species for ammonia oxidation reaction over Pt/Al₂O₃, but two kinds of intermediates, N₂H₄ and HNO, were observed for Pt/CeZrO₂. It consequently resulted in the obvious distinction of the NH₃-SCO catalytic performance; the light-off temperatures of NH₃ over Pt/Al₂O₃ and Pt/CeZrO₂ were 231 and 275 °C, respectively, while the maximum N₂ selectivity (65%) was obtained over Pt/CeZrO₂, it was obviously better than that over Pt/Al₂O₃.