Unraveling the Mechanistic Origin of High N₂ Selectivity in Ammonia Selective Catalytic Oxidation on CuO-Based Catalyst

Abstract

NH₃ emissions from industrial sources and possibly future energy production constitute a threat to human health because of their toxicity and participation in PM_2.5 formation. Ammonia selective catalytic oxidation to N₂ (NH₃-SCO) is a promising route for NH₃ emission control, but the mechanistic origin of achieving high N₂ selectivity remains elusive. Here we constructed a highly N₂-selective CuO/TiO₂ catalyst and proposed a CuO_<i>x</i> dimer active site based on the observation of a quadratic dependence of NH₃-SCO reaction rate on CuO_<i>x</i> loading, ac-STEM, and <i>ab initio</i> thermodynamic analysis. Combining this with the identification of a critical N₂H₄ intermediate by in situ DRIFTS characterization, a comprehensive N₂H₄-mediated reaction pathway was proposed by DFT calculations. The high N₂ selectivity originated from the preference for NH₂ coupling to generate N₂H₄ over NH₂ dehydrogenation on the CuO_<i>x</i> dimer active site. This work could pave the way for the rational design of efficient NH₃-SCO catalysts.