The difference in the active sites for CO2 and CO hydrogenations on Cu/ZnO-based methanol synthesis catalysts

The effect of Zn in copper catalysts on the activities for both CO2 and CO hydrogenations has been examined using a physical mixture of Cu/SiO2 + ZnO/SiO2 and a Zn-containing Cu/SiO2 catalyst or (Zn)Cu/SiO2. Reduction of the physical mixture with Hz at 573-723 K results in an increase in the yield of methanol produced by the CO2 hydrogenation, while no such a promotion was observed for the CO hydrogenation, indicating that the active site is different for the CO2 and CO hydrogenations. However, the methanol yield by CO hydrogenation is significantly increased by the oxidation treatment of the (Zn)Cu/SiO2 catalyst. Thus it is concluded that the Cu-Zn site is active for the CO2 hydrogenation as previously reported, while the Cu-O-Zn site is active for the CO hydrogenation.