Thermodynamic Stability, Redox Properties, and Reactivity of Mn3O4, Fe3O4, and Co3O4 Model Catalysts for N2O Decomposition: Resolving the Origins of Steady Turnover

Abstract

Manganese, iron, and cobalt model spinel catalysts were systematically investigated for understanding the roots of their divergent performance in N2O decomposition. The catalysts were characterized by XRD, RS, N2-BET, SEM, and STEM/EELS techniques before and after the reaction. Their redox properties and the thermodynamic stability range were thoroughly examined by survey and narrow scan TPR/TPO cycles. The results were accounted for by the constructed size-dependent Ellingham diagrams. It was shown that Fe3O4 and Mn3O4 spinels exhibit redox-labile Mn2+/Mn3+ and Fe2+/Fe3+constituents, and under the conditions of the deN2O reaction these catalysts have a pronounced tendency for stoichiometric overoxidation. The redox properties of Co3O4 are highly anisotropic, with Co2+ being reluctant to undergo oxidation but Co3+ being prone to easy reduction. The stability of the Co3O4 catalyst is then controlled by partial reduction of octahedral Co3+ cations, due to the surface oxygen release at elevated temperatures ...