Synergism between Cu and Zn sites in Cu/Zn catalysts for methanol synthesis

Abstract

Three Cu-based catalysts prepared using RF plasma-sputtering (Cu/ZnO and Cu/Al2O3) and coprecipitation (Cu/Zn/Al oxide) methods were employed for the investigation of the synergism between Cu and Zn sites. The static secondary ion mass spectrometry (SIMS) experiments indicate that, on both Cu/ZnO/Al2O3 and Cu/ZnO catalysts, CO is adsorbed at Cu sites (SIMS peaks appear at 91 and 93 amu), and H is bound to ZnO sites (67, 69, 70, 71 and 81, 83, 84, 85 amu) when the catalyst surfaces are exposed to H2, CO and CO2. Methoxy, the intermediate species of methanol synthesis, is found to be bound at Zn sites (95, 97, 98, 99 amu). CO and CO2 are found to induce Zn migration from sub-layers to the topmost layer while H2 is heterolyzed easier due to the presence of Cu. The coexistence of ZnO with Cu could enhance the capability of Cu to adsorb CO species and itself to adsorb H2 species. Al2O3 shows no synergetic effect with Cu in this experiment. No CO and H2 are detected on the Cu/Al2O3 catalyst exposed to syngas. The synergetic effect between Cu and Zn in the course of methanol synthesis was discussed.