The role of lattice oxygen in CO2 hydrogenation to methanol over La1-xSrxCuO catalysts

Abstract Catalytic CO2 hydrogenation to methanol has become an interesting carbon dioxide utilization process because it provides a solution to the environmental greenhouse gas problem with an economic benefit. Cu-based catalysts have been widely studied for this process and perovskite structured materials emerged as an interesting alternative to conventional supported catalysts, due to its oxygen mobility property and structural feasibility in enhancing CO2 adsorption capacity by simple doping with alkali metal oxides. The role of CO2 adsorption strength in promoting CO2 hydrogenation to methanol activity was investigated over perovskite structure derived LaxSr1-xCu1.0O materials. Among all of the Sr-modified catalysts, La0.9Sr0.1CuO has achieved the best performance with respect to CO2 conversion (8.59%) and methanol selectivity (49%) at 300 °C and 3.0 MPa pressure. Furthermore, La0.9Sr0.1CuO also displayed a stable catalytic performance for the tested period of 24 h with no carbon formation during CO2 hydrogenation reaction. The formation of perovskite structures in calcined catalysts was confirmed by XRD analysis. XPS analysis revealed a higher amount of lattice oxygen species for reduced La0.9Sr0.1CuO than others. Moreover, a correlation between the amount of lattice oxygen and methanol yields indicates the crucial role of lattice oxygen species in promoting methanol selectivity during CO2 hydrogenation reaction. The role of oxygen lattice was further investigated using other characterization techniques such as H2-TPR, CO2/O2-TPD, N2O pulse, and XAS experiments. The in situ CO/(CO2+H2) DRIFTS further confirmed the contribution of lattice oxygen and basicity in methanol selectivity.