A titration method was developed to quantify oxygen vacancies on the surface of indium oxide catalysts. The corresponding CO2 hydrogenation performance scaled with the number of vacancies on In2O3 samples. Atomic layer deposition was applied to tune the abundance of oxygen defects, resulting in enhanced methanol formation rates compared to catalysts prepared by incipient wetness impregnation.
The direct hydrogenation of CO2 to methanol is an attractive approach to employ the greenhouse gas as a chemical feedstock. However, the commercial copper catalyst, used for methanol synthesis from CO-rich syngas, suffers from deactivation at elevated CO2 partial pressure. An emerging alternative is represented by In2O3 as it withstands the hydrothermal conditions induced by the reverse water-gas shift reaction. The active sites for the adsorption of CO2 and the subsequent conversion into methanol were shown to be oxygen vacancies on the surface of In2O3. In this study, N2O was utilized as a probe molecule to quantify the number of vacancies on indium oxide catalysts. The number of inserted oxygen atoms could be correlated to the respective CO2 hydrogenation activity. Furthermore, the atomic efficiency of indium was enhanced by applying atomic layer deposition of indium oxide on ZrO2.Zum Volltext