CO₂ Hydrogenation Over In₂O₃

CO₂ hydrogenation is an important part of utilization of CO₂ which is one of the most popular topics in the world. Synthesizing highly valuable industrial products through CO₂ hydrogenation is considered a profitable way. Thus, the study of the reaction mechanism of CO₂ hydrogenation is very instructive to industry. Many scientists and researchers devoted themselves to prepare catalysts with good performance for CO₂ hydrogenation and further study the reaction mechanism in detail. Herein, we reported the synthesis of In₂O₃ with different structures and their activity and selectivity in CO₂ hydrogenation under both ambient pressure and high pressure. Moreover, mechanism of the reaction was discussed as well.In₂O₃ of various structures is prepared by solvothermal synthesis and calcination at different temperature. Powder X-ray diffraction?XRD?, scanning electron microscope?SEM?, and transmission electron microscope?TEM? were used to characterize the structure of the synthesized In₂O₃, which indicates that In₂O₃ prepared by solvothermal synthesis has both cubic and hexagonal structure, while only cubic structure is observed for the In₂O₃ prepared by calcination. Moreover, it turned out that calcination temperature has no effect on the structure of In₂O₃. CO₂ adsorption and desorption study by in situ Fourier transform infrared spectroscopy?in situ-FTIR? indicates that cubic and hexagonal In₂O₃ synthesized by both of solvothermal method and calcination have good performance on the absorption of CO₂. However, In₂O₃ prepared by solvlthermal synthesis has better desorption of CO₂, while In₂O₃ synthesized by calcination does not provide a decent performance on CO₂ desorption.In₂O₃ prepared by solvothermal synthesis performs good activity and stability in CO₂ hydrogenation reactions under ambient pressure, while In₂O₃ synthesized by calcination shows lower activity and becomes deactivation due to high temperature. Then In₂O₃ prepared by solvothermal synthesis is applied on the CO₂ hydrogenation reactions under high pressure. By studying the performance of the catalyst under the pressure from 1MP to 4MPa, it turns out that the increase of temperature and raise of pressure can improve the conversion rate of CO₂. The raise of pressure improves the selectivity of CH3 OH, however, the increase of temperature does not necessarily boost the conversion of CH3 OH. It has the highest yield of CH3 OH around 310³30 ?. Even the pressure is added to 4Mpa, while the major product of the reaction is CO. The cubic and hexagonal In₂O₃ prefers to reverse water-gas sift?RWGS? route rather than forming formate and then forming CH3 OH.In order to know the temperature that cubic In₂O₃ start to lose their activity, In₂O₃ synthesized by calcination is applied to CO₂ hydrogenation in ambient pressure at 400 ??500 ??600 ??700 ? for 360 minutes. The activity of In₂O₃ begins to decrease when the temperature is improved to 500 ? and exhausts at 700 ?. In₂O₃ synthesized by calcination is appropriate for the reaction that proceeds in the temperature below 500 ?.