The role of metal nanostructure in ceria-supported catalysts for ammonia oxidation to nitrous oxide

Abstract

Manganese (Mn) and chromium (Cr) catalysts supported on CeO₂ enable direct ammonia oxidation to nitrous oxide, N₂O, but the lack of synthesis-structure-performance relations hinders rational catalyst design. Herein, we generate a platform of CeO₂-supported Mn and Cr catalysts, systematically varying the metal nanostructure from single atoms to nanoparticles, and the carrier redox properties, as confirmed by advanced characterization methods. Surface reducibility of CeO₂ emerges as a general descriptor, controlling N₂O productivity. Conversely, structure sensitivity is metal specific, with Mn-based systems achieving high N₂O selectivity in single-atom and nanoparticle forms, while the selectivity of Cr-based systems is dependent on metal dispersion. In situ UV-visible (UV-vis), steady-state, and transient kinetic studies unveil the ability of redox-active MnO_x to synergize with CeO₂ and enhance oxygen transport for the reaction following a Mars-van Krevelen mechanism. This work provides fundamental insights into the role and function of each catalyst component and guidelines for the development of improved N₂O synthesis catalysts.