Comparative study on the effect of different copper loading on catalytic behaviors and activity of Cu/ZnO/Al2O3 catalysts toward CO and CO2 hydrogenation

Abstract

The ternary Cu/ZnO/Al2O3 (CZA) catalysts having different Cu loading were prepared by the co-precipitation method. Then, they were used in CO and CO2 hydrogenation to produce methanol under atmospheric pressure at 250 °C. The high Cu loading CZA catalyst (CZA-H) resulted in the enhancement of structural features and textural properties (e.g., BET surface area and the crystallite size of copper species). Furthermore, the conversion of CO and CO2 over CZA-H catalyst was apparently higher than that of the CZA-L (low Cu loading) catalyst. The major product of CO hydrogenation obtained from both catalysts was methanol, whereas in CO2 hydrogenation, the main product was CO. Deactivation of catalysts was also crucial during CO and CO2 hydrogenation. Therefore, the spent catalysts were determined to identify the nature of carbon formation. It revealed that amorphous and graphitic cokes were present. These cokes have different mechanisms in the elimination from the surface leading to influencing the deactivation process. The spent CZA-L was found to have higher carbon content, which was around 2.3% and 3.1% for CO and CO2 hydrogenation, respectively. Besides the amorphous coke, the graphitic coke was also observed in CZA-L after time on stream for 5 h.