Performance and Stability of Corundum-type In₂O₃ Catalyst for Carbon Dioxide Hydrogenation to Methanol

Carbon dioxide hydrogenation to methanol is a key chemical reaction to store energy in chemical bonds, using carbon dioxide as an energy sink. Indium oxide is amongst the most promising candidates for replacing the copper and zinc oxide catalyst, which is industrially applied for syngas mixtures but less idoneous for educts with carbon dioxide due to instability reasons. The polymorph of indium oxide and the operating conditions remain to be optimized for optimal and stable performance. Indium oxide catalysts containing different rhombohedral and cubic phase ratios were synthesized using a solvothermal method and evaluated in an ideally mixed gas phase reactor. The pure rhombohedral catalyst shows the best performance in terms of yield to methanol, selectivity, and stability. The phase stability was assessed using synchrotron in situ XRD and Rietveld refinement, shedding light on the stability of the different phases at extended operating conditions. Depending on the flow rate, temperature, and hydrogen partial pressure, a rhombohedral to cubic transition occurs, ultimately yielding inactive metallic indium. If present, cubic In₂O₃ serves as nuclei to induce the cubic to rhombohedral transition, hampering performance. These results allow for a more rational catalyst design and fine-tuning of the operating conditions to ensure optimal and stable performance.