Role of Calcination Temperatures of ZrO₂ Support on Methanol Synthesis from CO₂ Hydrogenation at High Reaction Temperatures over ZnOx/ZrO₂ Catalysts

Methanol synthesis from CO2 hydrogenation at high temperatures was investigated over ZnOx/ZrO2 catalysts to illustrate the role of calcination temperatures (600–1000 °C) of the ZrO2 support. Characterization results revealed that a ZnOx/ZrO2 solid solution (Zn–O–Zr) was formed for all catalysts. The formation of the ZnOx/ZrO2 solid solution was related to an enhancement of weak CO2 adsorption. The ZnZr catalyst with the ZrO2 calcined 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 CO2 could 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.