Methane Photoactivation on Copper Molybdate. An EXperimental and Theoretical Study

Article abstract of DOI:10.1021/j100310a019

It is shown that the activity of UV-irradiated MoO3 for the partial oxidation of methane in the presence of O2 at 100 deg C, leading to methanol formation, is markedly enhanced when Cu^II is added to the catalyst.The rate of methanol formation is maximum when the concentrations of copper and molybdenum are equal.Visible light activates CuMoO4 but not MoO3.We have made a molecular orbital study of the photoactivity of CuMoO4 toward hydrogen abstraction from methane at O^- centers.The activity of CuMoO4 in the visible region is assigned to O 2p - Cu 3d excitations; the Cu 3d band levels lie below the Mo 4d band and the orbitals have a large O 2p component.Mechanisms are proposed for increasing the lifetimes of the electron-hole pairs and thereby account for the synergistic effect in CuMoO4 which shows enhanced photoactivity compared with either CuO, which is photoinactive, or MoO3.Empty band-gap orbitals serve to stabilize homolytic H^. and ^.CH3 adsorption on O^2- sites relative to MoO3, and filled band-gap orbitals stabilize homolytic adsorption on Mo^VI sites.Heterolytic adsorption on Mo^VI and O^2- sites is stable but not on Cu^II and O^2- sites.Homolytic adsorption is unstable on Cu^II sites.