Stable and Active Oxidation Catalysis by Cooperative Lattice Oxygen Redox on SmMn₂O₅ Mullite Surface

Abstract

The correlation between lattice oxygen (O) binding energy and O oxidation activity imposes a fundamental limit in developing oxide catalysts, simultaneously meeting the stringent thermal stability and catalytic activity standards for complete oxidation reactions under harsh conditions. Typically, strong O binding indicates a stable surface structure, but low O oxidation activity, and <i>vice</i> <i>versa</i>. Using nitric oxide (NO) catalytic oxidation as a model reaction, we demonstrate that this conflicting correlation can be avoided by cooperative lattice oxygen redox on SmMn₂O₅ mullite oxides, leading to stable and active oxide surface structures. The strongly bound neighboring lattice oxygen pair cooperates in NO oxidation to form bridging nitrate (NO₃^-) intermediates, which can facilely transform into monodentate NO₃^- by a concerted rotation with simultaneous O₂ adsorption onto the resulting oxygen vacancy. Subsequently, monodentate NO₃^- species decompose to NO₂ to restore one of the lattice oxygen atoms that act as a reversible redox center, and the vacancy can easily activate O₂ to replenish the consumed one. This discovery not only provides insights into the cooperative reaction mechanism but also aids the design of oxidation catalysts with the strong O binding region, offering strong activation of O₂, high O activity, and high thermal stability in harsh conditions.