ZnO-In2O3 solid solution hollow tube improved CO2 hydrogenation to methanol via the formate route

Three ZnO-In2O3 solid solution hollow tube catalysts with different microstructure were synthesized for CO2 hydrogenation to methanol. ZnO could maintain In2O3 hollow tube structure from being destroyed during the reaction, and the ZnO-In2O3 solid solution could be in-situ formed on three catalysts during CO2 hydrogenation reaction. Especially, the structure of ZnO-In2O3 HT-I was most conducive to the creation of ZnO-In2O3 solid solution. The ZnO-In2O3 solid solution promoted electron transfer from ZnO to In2O3, resulting in an increase in the electron density of In2O3 surface and local electron imbalance around the oxygen vacancy. ZnO facilitated electron delocalization in surface lattice oxygen. The surface electrons were transferred and concentrated on surface oxygen vacancy, which enhanced the electron density of surface oxygen vacancy especially for ZnO-In2O3 HT-I catalyst. The "quality" of surface oxygen vacancy was raised, which boosted the adsorption and activation of H2 and CO2. The density functional theory (DFT) findings suggested that ZnO-In2O3 solid solution caused the energy barrier of formate species to be lowered and those of carboxylate species to be raised, which was more favorable for methanol generation. Combined experimental and DFT data proved that the CO2 hydrogenation to methanol proceeded via formate reaction route. Among the three ZnO-In2O3 catalysts, ZnO-In2O3 HT-I showed the highest methanol formation activity with 13.9% CO2 conversion and 68% methanol selectivity at 350 °C, and the methanol space–time yield (STY) reached 1.12 gMeOH h−1 gcat−1.