The effect of CO2 and H2 adsorption strength and capacity on the performance of Ga and Zr modified Cu-Zn catalysts for CO2 hydrogenation to methanol

Abstract

The hydrogenation of CO2 to methanol was performed over Ga2O3 and ZrO2 modified Cu-Zn based catalysts. The prepared catalysts were characterised via P-XRD, ICP-OES, BET, SEM-EDX, H2-TPR, CO2-TPD, H2-TPD and H2-chemisorption. The focus of this investigation was to assess the role of Ga2O3 and ZrO2 promoters on improving the methanol productivity over the Cu-Zn based catalysts. Emphasis was placed on the differences in CO2 and H2 adsorption capacity and strength due to the introduction of the modifiers, with a focus on the influence of these properties on methanol production. The ZrO2 promoted catalyst delivered a higher methanol space-time yield (STY) in comparison to the Ga2O3 promoted and unpromoted catalysts. The better catalytic performance of the ZrO2 modified catalyst was partly attributed to an improvement of the reducibility. Furthermore, the CO2-TPD results showed that the ZrO2 modified catalyst exhibited the highest CO2 uptake and adsorption strength which contributed to its higher methanol yield. A correlation between the quantity of the spillover hydrogen and methanol yield was also shown to exist for the prepared catalysts. The results obtained from this study suggested that a strong interaction between CO2 and the catalyst surface is crucial to avoid premature desorption of CO2 or its intermediates, thus improving the efficiency of the catalyst. In contrast, an intermediate interaction of H2 with the catalyst surface facilitates the hydrogen spill-over, which improves the methanol yield.