Good things come in threes - Nitrous oxide decomposition on Rh-Ce-Co oxide

Rh- and Co₃O₄-based catalysts are among the best materials to activate the N₂-O bond of nitrous oxide at low temperature and accomplish N₂O decomposition. In this work we have combined Ce with these two components to obtain dispersed RhO_x and CeO_x on Co₃O₄ to exploit potential multicomponent interfacial properties. RhO_x-CeO_x-CO₃O₄ exhibits the best catalytic performance relative to the bi-component catalysts and is non-additive, which is attributed to the modulation of the Co and Rh oxidation states at a synergistic Rh–O–Co–O–Ce interface identified by characterization methods and density functional theory. We have used kinetic analysis and repeated N₂O pulses in the modulated excitation approach to obtain indication on the reaction mechanism from XANES and found that RhO_x species oxidize in N₂O simultaneous to reduction of CoO_x species. DFT indicates that the proximity of the Ce 4f and Rh 4d states, mediated by oxygen atoms, effectively couples Ce to Rh, in agreement with the increased content of Ce³⁺ from XPS. Also, the upward displacement of the Ce 4f* level toward the Co 3d* states strengthens the Ce–Co antibonding overlap, with the interconnecting oxygen atoms enabling efficient redox communication. This integrated network produces stabilized Rh species in a higher oxidation state that is confirmed by XPS and XANES. Therefore, N₂O decomposition on this type of catalyst proceeds through a multi-site, cooperative Mars-van Krevelen pathway, in which Co₃O₄–CeO₂ acts as an oxygen reservoir enabling the redox cycling of RhO_x.

This study highlights the ability of mixed metal oxide catalysts to exploit interfacial effects to achieve improved activity in redox-mediated reactions and offers a rationale for the engineering of mixed metal oxide catalysts guided by operando spectroscopy.

For more information, the full study can be accessed here.