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

CO 2 to methanol is an important reaction that reduces the concentration of CO 2 in the atmosphere. Ni/In 2 O 3 catalysts with three different In 2 O 3 morphologies, i.e. cube (c), hollow tube (h), and plate (p), were synthesized by an impregnation method and studied for CO 2 hydrogenation to methanol. It was found that the performance of the catalysts is closely related to the morphology of In 2 O 3 . At 300 °C, 2 MPa, and 16 L·g –1 ·h –1, the Ni/In 2 O 3 -h catalyst showed the highest space time yield of methanol of 18.73 mmol·g –1 ·h –1 . The morphology of In 2 O 3 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 CO 2 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 CO 2 to methanol may follow the formate pathway on the Ni/In 2 O 3 catalysts.