Exploring the dynamic evolution of lattice oxygen on exsolved-Mn₂O₃@SmMn₂O₅ interfaces for NO Oxidation.

Abstract

Lattice oxygen in metal oxides plays an important role in the reaction of diesel oxidation catalysts, but the atomic-level understanding of structural evolution during the catalytic process remains elusive. Here, we develop a Mn₂O₃/SmMn₂O₅ catalyst using a non-stoichiometric exsolution method to explore the roles of lattice oxygen in NO oxidation. The enhanced covalency of Mn-O bond and increased electron density at Mn³⁺ sites, induced by the interface between exsolved Mn₂O₃ and mullite, lead to the formation of highly active lattice oxygen adjacent to Mn³⁺ sites. Near-ambient pressure X-ray photoelectron and absorption spectroscopies show that the activated lattice oxygen enables reversible changes in Mn valence states and Mn-O bond covalency during redox cycles, reducing energy barriers for NO oxidation and promoting NO₂ desorption via the cooperative Mars-van Krevelen mechanism. Therefore, the Mn₂O₃/SmMn₂O₅ exhibits higher NO oxidation activity and better resistance to hydrothermal aging compared to a commercial Pt/Al₂O₃ catalyst.