CO ₂ Hydrogenation to Methanol over Ni/In ₂ O ₃ : Effects of In ₂ O ₃ Morphology

CO2 to methanol is an important reaction that reduces the concentration of CO2 in the atmosphere. Ni/In2O3 catalysts with three different In2O3 morphologies, i.e. cube (c), hollow tube (h), and plate (p), were synthesized by an impregnation method and studied for CO2 hydrogenation to methanol. It was found that the performance of the catalysts is closely related to the morphology of In2O3. At 300 °C, 2 MPa, and 16 L·g–1·h–1, the Ni/In2O3-h catalyst showed the highest space time yield of methanol of 18.73 mmol·g–1·h–1. The morphology of In2O3 affects the state of Ni species on its surface, and highly dispersed Ni species, rather than single-atom Ni species or aggregated Ni species, are considered as active sites in CO2 hydrogenation to methanol. The appropriate quantity of oxygen vacancies is also an important factor affecting the performance of the catalysts. In-situ diffuse reflectance infrared Fourier-transform spectroscopy measurements suggest that hydrogenation of CO2 to methanol may follow the formate pathway on the Ni/In2O3 catalysts.