Influence of Phase Transitions in Indium-Based Catalysts for the Catalytic Performance in CO2 Hydrogenation to Methanol

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This study investigates the phase-transition behavior of indium-based catalysts under methanol-synthesis conditions and demonstrates that preforming strongly affects catalytic performance. In situ X-ray diffraction (XRD) revealed that In(OH)3 fully dehydrated to In2O3 at 275 °C under high methanol conversion conditions, while neat In2O3 remained stable. Supporting the hydroxide on ZrO2 significantly lowered its phase-transition temperature, bringing it below 200 °C. Rietveld refinement and phase quantification revealed the presence of small amounts of hydroxide under reaction conditions, indicating an In2O3–In(OH)3 dynamic equilibrium. Preforming the In(OH)3/ZrO2 with hydrogen revealed that the bulk hydroxide converts to the oxide at 125 °C. Thermogravimetric analysis (TGA) indicated delayed water release starting at 150 °C. This suggests that oxygen vacancies can only form after water desorption. This is evident in catalytic testing, where preforming conditions significantly influence catalytic activity. Preforming with hydrogen above the phase-transition temperature resulted in a more active catalyst. The same trend was also confirmed with a Ni-doped catalyst, achieving a maximum methanol productivity of 0.49 gMeOH gcat h–1 at 300 °C and 75 bar with a gas mixture consisting of 50% N2, 12.5% CO2, and 37.5% H2. These findings reveal further potential of the indium-based methanol synthesis catalyst by improving catalyst pretreatment and better understanding the properties of catalyst phase transitions.