In2O3 crystal phase variation on In2O3/Co3O4 to boost CO2 hydrogenation to methanol.

• In 2 O 3 phase in In 2 O 3 /Co 3 O 4 can be regulated via altering citric acid content in the impregnation process. • With the help of Co0, h-In 2 O 3 is partially transformed into c-In 2 O 3 during reaction reconstruction. • c-In 2 O 3 has stronger interaction with metal Co0 than h-In 2 O 3. • More oxygen vacancies are formed in c-In 2 O 3 /Co 3 O 4 while stronger CO adsorption ability is achieved in h-In 2 O 3 /Co 3 O 4. • CO 2 conversion and methanol selectivity are directly related to the In 2 O 3 crystal phase for In 2 O 3 /Co 3 O 4. In 2 O 3 /Co 3 O 4 catalysts with various crystal structure of In 2 O 3 were successfully prepared by means of regulating the amount of citric acid, and were applied for CO 2 hydrogenation to methanol to understand the structure-activity relationship. With the increase of citric acid content in the impregnation process, hexagonal In 2 O 3 (h-In 2 O 3) is gradually transformed into cubic In 2 O 3 (c-In 2 O 3). The interaction and electron transfer between c-In 2 O 3 and Co 3 O 4 are stronger than those between h-In 2 O 3 and Co 3 O 4. In the In 2 O 3 /Co 3 O 4 catalysts prepared with citric acid, phase transformations were observed under reaction conditions of 4 MPa and 300 °C. Initially, h-In 2 O 3 transitions into c-In 2 O 3. Concurrently, there is a transformation of In 2 O 3 and Co 3 O 4 into metallic cobalt (Co0) and the compound Co 3 InC 0.75. Except for h-In 2 O 3 /Co 3 O 4 containing mixed h-In 2 O 3 and c-In 2 O 3 , In 2 O 3 in all other catalysts exists in the form of c-In 2 O 3. Owing to stronger interaction between c-In 2 O 3 and Co0, dissociated hydrogen atoms diffuse more easily from the metallic Co0 to c-In 2 O 3 to produce more oxygen vacancies, accompanied with the formation of more inactive Co 3 InC 0.75 (70 wt% for c-In 2 O 3 /Co 3 O 4 vs 58 wt% for h-In 2 O 3 /Co 3 O 4). However, h-In 2 O 3 /Co 3 O 4 has stronger adsorption ability of CO to improve methanol selectivity. Thus, it can be observed that the CO 2 conversion and methanol selectivity of the catalyst are directly related to the In 2 O 3 crystal phase for In 2 O 3 /Co 3 O 4 catalysts. To be specific, h-In 2 O 3 /Co 3 O 4 has the higher selectivity of methanol, while c-In 2 O 3 /Co 3 O 4 exhibits the higher conversion of CO 2 and methanol space-time yield. [Display omitted] [ABSTRACT FROM AUTHOR]