Comparative studies of manganese-doped copper-based catalysts: the promoter effect of Mn on methanol synthesis

A Mn-promoted Cu/ZnO/Al2O3 catalyst with 5-10% improvement in methanol yield as compared with the undoped Cu/ZnO/Al2O3, catalyst under identical conditions has been synthesized. In order to understand the promoter effect of Mn on the methanol production, Cu/Al2O3, and Cu/SiO2, catalysts with and without various amounts of Mn were also prepared and comparatively investigated by microreactor, N2O titration, TPR (Temperature Programmed Reduction) and XPS (X-ray Photoelectron Spectroscopy). Experimental results show that these Mn-promoted catalysts have higher catalytic activity, larger surface Cu concentration, and elevated Cu reduction temperature than their Mn-undoped counterparts. XPS study gives evidence that in the reduced or reacted catalysts, the interaction between Mn and Cu occurs, resulting in the reduction of Mn4+ to Mn2+ or Mn3+, as well as the oxidation of Cu-0 and Cu+ to higher oxidation states. This interaction may be responsible for the harder Cu reduction process, better Cu dispersion, higher active center concentration, and thus enhanced methanol yield. (C) 1998 Elsevier Science B.V.