DFT study on the active sites in Mn-Na72WO4/SiO2 catalyst

Mn-Na2WO4/SiO2 is one of the best catalysts for oxidative coupling of methane. To investigate the nature of active centers and the reaction mechanism, the structure of possible metal sites formed by tungsten and manganese over the silica surface were studied using molecular simulation method and ab initio DFT calculations. Silica support exists in the catalyst as alpha -cristobalite and its (111) face exposes preferentially to the surface. The calculated results show that tungsten interacts with the silica surface by three or one bridge oxygen atoms to form tetrahedral [WO4], and manganese interacts with single bridge oxygen to form dispersed [MnO4] or exists as oxide clusters. The nature of the molecular orbitals and the electronic structure suggest that the tetrahedral [WO4] site with single bridge oxygen is the most probable active center responsible for methane activation.