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 MnOx 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.