Bridge-type Mn-O-Mn sites promoting catalytic methane oxidation and carbonate desorption over Mn-based oxides

MnO 2 is a good catalyst due to its various crystal structures and oxidative valence states. The relationship between the surface structure and activity of MnO 2 at low temperatures has been reported, but the structure-activity relationship between its crystal structure and catalytic activity at high temperatures is unclear. In this study, α-, γ-, and δ-MnO 2 catalysts were used for catalytic methane (CH 4 ) oxidation. α-MnO 2 had better CH 4 conversion (95%) and CO 2 selectivity (100%) at 600 °C due to its large amount of bridge-type oxygen (Mn-O-Mn). DFT calculation results showed that the adsorption energy of CH 4 at the surface oxygen site of the α-MnO 2 catalyst was the lowest. Operando TPR-DRIFTS-MS results showed that Mn-O-Mn played an important role in CH 4 oxidation. Mn-O-Mn favored O 2 decomposition and promoted terminal-type oxygen (Mn&z.dbd;O) formation. Monodentate carbonate was easily formed at Mn&z.dbd;O with CO oxidized by O in Mn-O-Mn. Mn-based catalysts with more Mn-O-Mn sites are of great significance for high-temperature CH 4 oxidation. MnO 2 is a good catalyst due to its various crystal structures and oxidative valence states.