The Influence of H 2 Activation on CO 2 Hydrogenation to Methanol over ZnO-Based Oxides

The activation of H2 is crucial for the hydrogenation of CO2 to various value-added chemicals, but mechanistic insights into the role of active H species remain underexplored. Here, we synthesized a series of ZnO-based binary oxides by varying the oxide supports for the hydrogenation of CO2 to methanol. Through a series of (quasi) in situ spectroscopic characterizations, we found that the concentration of surface H species is determined by the surface electronic structures of ZnO-based binary oxides. For hydrogen-deficient ZnO-based catalysts, CO2 was activated into carbonate species, followed by hydrogenation to formate species, which are key intermediates for methanol synthesis. In contrast, on the hydrogen-rich ones, CO2 was activated into bicarbonate species and ultimately hydrogenated to form CO. In addition, it was shown that the activated H species from ZnO were more effective in catalyzing the hydrogenation conversion of carbon-containing species compared to the H species adsorbed on oxide supports such as Al2O3. This work clarifies the fundamental principles that underlie the structure-dependent reaction pathways of CO2 hydrogenation on ZnO-based oxides, offering key guidance for tuning the selectivity of CO2 hydrogenation.