Reverse effect of metal-support interaction on platinum and iridium catalysts in ammonia selective oxidation

Ammonia emissions from vehicles and power plants cause significant environmental concerns. Here, a range of platinum and iridium catalysts supported on oxides with various levels of reducibility were investigated in ammonia selective catalytic oxidation. Weak metal-support interaction (MSI) led to the formation of metal nanoparticles on irreducible Al₂O₃, whereas strong MSI (SMSI) induced the generation of single-atom metals on reducible CeO₂. Notably, MSI demonstrated opposite effects on the catalytic performance of Pt-based catalysts (Pt/Al₂O₃ ≫ Pt/TiO₂ > Pt/CeO₂) and Ir-based catalysts (Ir/CeO₂ > Ir/TiO₂ ≫ Ir/Al₂O₃). Metallic Pt nanoparticles on Pt/Al₂O₃ activated gaseous O₂ and promoted the low-temperature NH₃ oxidation. Conversely, on Ir/CeO₂ catalysts, the single-atom Ir-O-Ce site demonstrated high reactivity for NH₃ cleavage with an extremely low energy barrier, contributing to the superior low-temperature activity. This study provides insights into governing the MSI effect to regulate the structure on active sites of supported catalysts, thereby enhancing their catalytic performance.