Effects of Compositional Changes of Cu/ZnO, Cu/Al2O3, and Cu/ZnO/Al2O3 Catalysts on Methanol Synthesis from CO2 Hydrogenation

Several copper catalysts were prepared, characterized, and tested for hydrogenation of CO 2 to produce methanol. The copper atoms in the Cu/ZnO catalyst occupy 24-33% of the surface area whereas only 5-15% of the copper in the Cu/Al 2 O 3 catalyst is on the surface of the catalyst by changing their mole ratio from 3:1 to 1:2. The surface area of Cu/Al 2 O 3 catalysts was three to four times larger than that of Cu/ZnO. Presence of Al 2 O 3 in the catalyst increased the maximum H 2 TPR peak about 30° higher than that of copper oxide only. Meanwhile, the presence of ZnO in the catalyst decreased the TPR maximum peak of Cu/ZnO about 20° lower than copper oxide only and resulted in high energy state of copper ion. TON (turnover number) of Cu/ZnO for methanol synthesis from CO 2 /H 2 gas was higher than that of Cu/Al 2 O 3 The methanol selectivity of Cu/Al 2 O 3 catalyst was slightly higher than that of Cu/ZnO. The conversion of CO 2 was proportional to surface area of copper. TON per copper atom.h for CO 2 hydrogenation increased as copper content decreased.