Mn-Na_2WO_4/SiO_2催化剂表面活性中心结构的DFT研究

DFT Study on the Active Sites in Mn-Na_2WO_4/SiO_2 Catalyst

利用密度泛函方法 (DFT)研究了 Mn-Na2WO4/SiO2催化剂表面的活性中心结构 .计算表明 ,在α-方石英的 (111)面上 ,W能以单个或三个桥氧与载体作用形成稳定的四面体配位结构 ,Mn则能以单个桥氧与载体配位或形成不同结构的氧化物团簇；以单个桥氧担载的 [WO4]四面体是最可能的甲烷活化中心 .

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 asα-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.