Active site proximity regulates selectivity in ammonia oxidation reactions

Metal-oxide catalysts have attracted significant attention in ammonia (NH₃) oxidation reactions, including selective catalytic reduction (SCR) of nitrogen oxides (NOx) and selective catalytic oxidation (SCO) of NH₃. However, minimizing the formation of nitrous oxide (N₂O) remains a key challenge. In this study, we demonstrate that the oxidation behavior and consequently N₂O selectivity can be effectively tailored by controlling the nuclearity of supported metal oxides. Comparative studies between isolated Mn single sites and MnOx nanoclusters with similar oxidation states, coordination numbers, and supported in the same substrate, reveal that isolated Mn sites significantly suppressed the formation of N₂O. In contrast, MnOx nanoclusters generate higher amounts of N₂O. This structure-selectivity relationship extends beyond the Mn/TiO₂ system, with similar proximity-dependent behavior observed in Co- and Ni-oxide materials in NH3-SCR of NO reaction. These findings offer valuable insights for the rational design of metal-oxide catalysts with reduced N₂O emissions in NH₃ oxidation processes.