CuO-MgO/SiO₂ Catalysts Prepared By Adsorption Phase Reaction Technique For Low Temperature Methanol Synthesis In Liquid Phase

The one-pass conversion of syngas to methanol on current commercial condition is limited at a low level of 20% by thermodynamics since the reaction is extremely exothermic and the heat transmission of fixed bed is not favorable. In recent years, low-temperature methanol synthesis in liquid-phase, because of good heat transfer performance, has been well studied. The reaction process is considered to include two main steps of carbonylation and hydrogenation where the liquid phase is alcohol. The catalytic action and influence mechanism of Cu-based catalysts in methanol synthesis are not very clear. In previous research, Cu/SiO2 catalysts with high carbonylation activity were prepared, and in this dissertation, hydrogenation activity of CuO-MgO/SiO2 catalysts prepared by adsorbed-layer reactor technique was studied.TiO2, Al2O3, MgO and ZnO were loaded on first layer as modify components of SiO2 to suppress the strong combination between CuO and SiO2. It was found that MgO, ZnO and TiO2 showed better carbonylation activity, while only CuO showed hydrogenation activity. The preloaded MgO helped improve the hydrogenation activity. XRD, H2-TPR and XPS indicated there existed interaction between loaded components, which leaded to crystallinity of CuO decreasing, reduction temperature reducing and binding energy of Cu 2p3/2 shifted to lower direction. By regulating the amount of preloaded MgO, the relationship between Cu-Mg interaction and hydrogenation activity was found.Varied loading methods may have an effect on Cu-Mg interaction. Cu and Mg were highly dispersed on surface of carriers when CuO and MgO were loaded together, and the interaction between CuO and MgO strengthened, as a consequence the hydrogenation activity improved. As the amount of MgO in second layer increased, Cu-Mg interaction grew, however, active sites of Cu would be covered by MgO when loaded MgO was too much. So the hydrogenation activity showed a maximum value. In this dissertation, the influence of different feed-in ways, adsorbed water volume and reaction temperature on hydrogenation activity were studied. The results of characterization and catalytic reaction showed, it was the interaction between loaded components rather than the particle size and dispersity of catalysts that mainly influenced the hydrogenation activity. Since the Cu species interacted with MgO were the active sites, proper preparation condition would lead to stronger interaction, and such catalysts showed better hydrogenation activity.