Effect of the Preparation Methods on the Physicochemical Properties of Indium-Based Catalysts and Their Catalytic Performance for CO2 Hydrogenation to Methanol

Indium oxides (In2O3) and indium oxides supported zirconia (ZrO2) have been known possible alternatives for conventional copper-based catalysts in the CO2-hydrogenation to methanol. This study aims to investigate the effect of preparation techniques on the physicochemical properties of indium-based materials and their catalytic performance for the hydrogenation of CO2 to methanol. Two series of both single oxide In2O3 and binary In2O3-ZrO2 have been synthesized by combustion, urea hydrolysis, and precipitation with different precipitating agents (sodium carbonate and ammonia/ethanol solution). Physicochemical properties of materials are characterized by elemental analysis, XRD, N-2 physisorption, SEM/EDX, micro-Raman, XPS, H-2-TPR, and CO2-TPD. Cubic In2O3 was the common phase generated by all four synthesis methods, except for urea hydrolysis, where rhombohedral In2O3 was additionally present. The combustion method produced the materials with the lowest specific surface areas while the precipitation using ammonia/ethanol aided in creating more oxygen defects. The synthesis methods strongly influenced the degree of interaction between the oxides and resulted in improvements in properties that boosted the catalytic performance of the binary oxides compared to their single-oxide counterparts.