Tuning adsorption properties of GaxIn2-xO3 catalysts for enhancement of methanol synthesis activity from CO2 hydrogenation at high reaction temperature

Light olefins can be produced from CO2 hydrogenation in a single reactor using a combination of a methanol synthesis catalyst and a methanol-to-olefin (MTO) catalyst. However, commercial methanol synthesis catalysts are active at low temperatures (200-260 degrees C), while MTO reaction is feasible at higher temperatures (> 300 degrees C). Herein, we report the CO2 hydrogenation to methanol at high temperatures (320-400 degrees C) over GaxIn2-xO3 catalysts. By tuning the Ga/In ratios, phase, crystallinity, pore structure, morphology, electronic properties as well as adsorptive properties of GaxIn2-xO3 catalysts can be modified. At the lowest temperature (320 degrees C), the pure In2O3 shows the highest methanol yield. However, the maximum methanol yield declines significantly with increasing reaction temperatures. Incorporation of Ga into the In2O3 crystal lattices at x = 0.4 (Ga0.4In1.6O3) maximizes the methanol yield at higher reaction temperatures of 340-360 degrees C. This enhancement can be attributed to an increased binding energy of adsorptive molecules with the catalyst surface to promote the hydrogenation of CO2 to methanol. Further increasing Ga content (x > 0.4) leads to greatly strengthen the binding for adsorptive molecules, resulting in a lower methanol yield and the formation of methane. The surface chemisorbed oxygen is found to be a key factor determining the CO yield.