Understanding surface structures of In2O3 catalysts during CO2 hydrogenation reaction using time-resolved IR, XPS with in situ treatment, and DFT calculations

The In2O3 catalyst has been shown to have a high activity for CO2 hydrogenation to methanol. For this high pressure process, reliable spectral assignment of surface species formed by interaction with CO2, H2O, and other major reaction ingredients, is the key step to achieve mechanistic understanding. In this study, in situ IR and XPS are performed to investigate the O1s binding energies of the adsorbates induced by CO2 and H2O treatments along with density functional theory (DFT) simulations to further correlate the calibrated assignments with surface structures. Time resolved IR indicates that carbonates formation induced by CO2 exposure replaces the original hydroxyl on In2O3, and XPS further reveals that these two oxygen species have very similar binding energies (532.0 ± 0.2 eV). Computational results using the In2O3(1 1 0) and (1 1 1) slab models give good agreement with the XPS experiments, further suggesting that the amount of oxygen vacancy concentration does not induce new lattice oxygen O1s binding energy, but resulting in a slight shift to a higher binding energy instead. Our results provide useful structure information for the In2O3 catalyst surface and shed light for further investigations into its kinetic behavior under methanol synthesis condition.