Differences in bifunctionality of ZnO and ZrO2 in Cu/ZnO/ZrO2/Al2O3 catalysts in hydrogenation of carbon oxides for methanol synthesis

This work investigates the promotional roles of ZrO2 and ZnO for methanol synthesis on five Cu6Zn3.0-xZrxAl1 (x = 0.0, 0.5, 1.5, 2.5, 3.0) catalysts in the various CO2 feed composition. TOF decreased with an increase in x of Cu6Zn3.0-xZrxAl1 catalysts in the 5% CO2 feed, while TOF is maximized over Cu6Zn1.5Zr1.5Al1 in the 100% CO2 feed. Both the effects of Zn (reverse spillover) and Zr (additional reaction sites) in the vicinity of Cu promote the CO2 hydrogenation, maximizing the catalytic activity of Cu6Zn1.5Zr1.5Al1 in the 100% CO2 feed. The migration of hydrogen on ZrO2 can be limited in little surface hydroxyls in 5% CO2 feed, which can be a reason for the negative role of ZrO2 in the 5% CO feed. The promotional effect of ZrO2 on Cu/ZnO is important only for high CO2 feed more than 50% CO2.