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/Al 2O 3) 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/Al 2O 3 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 H 2, CO and CO 2. Methoxy, the intermediate species of methanol synthesis, is found to be bound at Zn sites (95, 97, 98, 99 amu). CO and CO 2 are found to induce Zn migration from sub-layers to the topmost layer while H 2 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 H 2 species. Al 2O 3 shows no synergetic effect with Cu in this experiment. No CO and H 2 are detected on the Cu/Al 2O 3 catalyst exposed to syngas. The synergetic effect between Cu and Zn in the course of methanol synthesis was discussed.