Revealing the origin of high N2 selectivity in NH3 oxidation over copper-based acid catalysts via solid precursors surface modulation

The heterogeneity (acid sites) and stability (redox sites) of metal loss on metal-acid catalyst surfaces are the fundamental factors for the "trade-off" effect between activity and selectivity in the catalytic process with NH 3 as the activation precursor. However, the molecular-level impact of these surface characteristics on catalytic performance remains unclear and contentious. Herein, we propose a straightforward decomposition temperature control method, which operates below the single-layer dispersion threshold of solid sulfate/nitrate precursors. This method adjusts the micro-coordination electronic environment and work function of the active site by employing (2 H + )SO 4 2- species with negligible structural influence, thereby achieving precise control over the redox properties and acidity of metal-acid catalysts. In the NH 3 oxidation model reaction, ab initio molecular dynamics (AIMD) simulations show that even at 500 K, the (2 H + )SO 4 2- species can direct the dissociation of nearby adsorbed NH 3 into -NH 2 species. This is due to the (2 H + )SO 4 2- species can strip the electrons from the antibonding states below the Fermi level of the -NH 2 species via the high-position chemisorbed oxygen 2p orbitals, thereby reducing the electron state energy of the -NH 2 species through the -NH 2 -1s-2p-(2 H + )SO 4 2- bond, even these Brønsted strong acid sites does not participate in the low-temperature NH 3 oxidation. This prevents the over-oxidation of -NH 2 species, anchoring the nearby high-selectivity i-SCR intermediate. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results confirm that abundant -NH 2 species at high temperatures can overcome the spatial steric hindrance of (2 H + )SO 4 2- species, enhancing the N 2 selectivity via the i-SCR mechanism (-NH 2 + NO x /Nitrate → N 2 + H 2 O).