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 Mn(2)O(3)/SmMn(2)O(5) 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 Mn(3+) sites, induced by the interface between exsolved Mn(2)O(3) and mullite, lead to the formation of highly active lattice oxygen adjacent to Mn(3+) 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 NO(2) desorption via the cooperative Mars-van Krevelen mechanism. Therefore, the Mn(2)O(3)/SmMn(2)O(5) exhibits higher NO oxidation activity and better resistance to hydrothermal aging compared to a commercial Pt/Al(2)O(3) catalyst.