Experimental and theoretical insights into the support-dependent N2 selectivity of CuO-based NH3-SCO catalysts

Abstract

Selective catalytic oxidation of ammonia (NH₃-SCO) into harmless N₂ (instead of pollutant NO_x and greenhouse gas N₂O) is a promising technique for the removal of pollutant NH₃. The CuO-based NH₃-SCO catalyst has attracted significant research interest owing to its advantages in catalytic performance and cost, but it is still elusive how support material affects product selectivity, hindering the development of highly N₂-selective catalysts. Herein, we present a combined experimental and theoretical study using CuO/MO_x (M = Ti, Zr, and Ce) catalysts with different metal oxide supports to provide molecular-level understanding of support effects in NH₃-SCO. In situ spectroscopy and theoretical calculations revealed that variations in N₂ selectivity of these catalysts originated from their diverse preferences to competing reaction pathways. It was observed that the local coordination environments of the CuO_x active sites were tuned by the support material. This active site–support interaction could alter the energy barriers of key elementary reactions (N₂H₄* formation and NH₂* dehydrogenation), resulting in different product selectivity. Scaling relationships between the energy barriers of these key elementary reactions and two easily computed descriptors (the binding strength of key intermediates or reaction energies) were discovered, which could avoid the time-consuming process of transition state searching and enable rational design and fast screening of highly N₂-selective NH₃-SCO catalysts.