Role of Calcination Temperatures of ZrO2Support on Methanol Synthesis from CO2Hydrogenation at High Reaction Temperatures over ZnOx/ZrO2Catalysts

Methanol synthesis from CO2hydrogenation at high temperatures was investigated over ZnOx/ZrO2catalysts to illustrate the role of calcination temperatures (600–1000 °C) of the ZrO2support. Characterization results revealed that a ZnOx/ZrO2solid solution (Zn–O–Zr) was formed for all catalysts. The formation of the ZnOx/ZrO2solid solution was related to an enhancement of weak CO2adsorption. The ZnZr catalyst with the ZrO2calcined at 600 °C achieved the highest methanol selectivity (75.1%) at 300 °C, corresponding to the highest amount of weak basic sites. However, its methanol selectivity drastically declined as the reaction temperatures increased because the weakly adsorbed CO2could not be stabilized for hydrogenation to form methanol. A substantial reduction of weak basic sites was observed with ascending calcination temperature of ZrO2, enhancing methanol selectivity at elevated temperatures.