Insight into the roles of superoxide-type (Mn(-O-)2Mn), bridge-type (Mn-O-Mn), and terminal-type (Mn[dbnd]O) oxygen species on MnO2 of different crystal structures in CO oxidation using operando TPR-DRIFTS-MS

Abstract

MnO2 is a promising catalyst due to its abundant metal valence and good redox ability. Different crystal phases of MnO2 have different oxygen species, but the relationship between their catalytic activity and crystal structures is unclear. In this study, four MnO2 catalysts with crystal structures (α-, β-, γ-, and δ-MnO2) were selected to unveil the roles of terminal-type (MnO), superoxide-type Mn(-O-)2Mn, and bridge-type (Mn-O-Mn) oxygen species in CO oxidation. γ-MnO2 has the best CO oxidation performance. Density functional theory calculation results show that MnO on γ-MnO2 can adsorb CO easier than other two types of oxygen species. Operando TPR-DRIFTS-MS results show that MnO on the surface of γ-MnO2 can react with CO to form terminal-type oxygen vacancies (M2+=□2–) at low temperatures. Meanwhiles, Mn(-□-)(-O-)Mn and Mn-□-Mn can dissociate O2 to form MnO under certain conditions to promote CO oxidation. MnO2 catalysts with more MnO oxygen species are of great significance for CO oxidation at a low temperature.