Effect of Surface Hydroxyls on CO2 Hydrogenation Over Cu/γ-Al2O3 Catalyst: A Theoretical Study

Catalytic hydrogenation of CO2 to methanol is a promising way to recycle and utilize CO2. In this study, the elementary steps leading to HCOO and CO formation have been explored to identify hydroxylation effect of the oxide support on the selectivity in CO2 hydrogenation on Cu/gamma-Al2O3 catalyst by the density functional theory (DFT) slab calculations. Two models: Cu4 cluster supported on the dry gamma-Al2O3(110) surface, D(Cu4), and on the hydroxylated gamma-Al2O3(110) surface, H(Cu4), have been used to model Cu/gamma-Al2O3. On D(Cu4), the formation of HCOO is preferred kinetically. On H(Cu4), HCOO formation is still kinetically favorable. These results indicate that the hydroxylation of gamma-Al2O3 support cannot alter the pathway of CO2 hydrogenation forming the dominate product HCOO, and ultimately, the selectivity of CO2 hydrogenation for HCOO formation on Cu/gamma-Al2O3 is higher, which supports the experimental fact that Al2O3-supported Cu catalyst is widely used to synthesize methanol by CO2 hydrogenation.