Optimizing methanol synthesis from CO2: Are bulk hexagonal indium oxide structures superior to cubic ones?

Recently, catalysts based on bulk indium oxide (In 2 O 3) have been used in CO 2 valorization; however, several studies correlate crystal phase with performance without considering possible changes during the reaction. In this context, we investigated different crystal phases of bulk In 2 O 3 (pure cubic, hexagonal, or mixed-phased) in CO 2 hydrogenation, where we observed variations in catalytic activity associated with phase transitions occurring under reaction conditions. We systematically compared the crystal phase and surface area before and after the reaction, showing that, at 350°C, independent from the initial In 2 O 3 structure, there is a tendency to form the cubic phase accompanied by the loss of surface area. To reach these results, we employed various synthetic methods that tailored structural and textural characteristics to achieve desired properties; for the first time, we obtained a cubic major mixed-phase In 2 O 3 structure at a 3-hour synthesis time by using a microwave-assisted method. Such material presented the best methanol productivity. Thus, as not previously reported, our results revealed that utilizing bulk hexagonal In 2 O 3 may not be interesting under this temperature; also, a higher surface area does not necessarily provide improved conversion rates. XPS, XRD, EPR, MEV, N 2 physisorption, CO 2 -TPD, and H 2 -TPR were performed and corroborated our investigations. [Display omitted] • Tailored synthetic methodologies were used to obtain specific structural and textural characteristics of In2O3 catalysts. • Examination of pure cubic, hexagonal, or mixed-phased In2O3 and different surface areas in CO2 hydrogenation. • Our findings indicate that utilizing bulk hexagonal In2O3 might not be advantageous under a specified temperature condition. • Microwave urea decomposition synthesizes In2O3 with mostly cubic structure, presenting high oxygen vacancies generation. [ABSTRACT FROM AUTHOR]