To mitigate the CO2 emission, it’s highly desirable to convert CO2 to useful chemicals. Among the various approaches, designing the catalyst for CO2 hydrogenation to methanol is considered a useful strategy. Because, methanol is an industrially important precursor that is used for the production of other useful chemicals such as formaldehyde, olefins, etc. Commercially Cu-based catalysts have been utilized extensively for methanol production. However, their selectivity for the methanol is low because of the competing reverse water–gas shift (RWGS) reaction. Oxide-based catalysts such as In2O3 and ZnZrOx were also proposed for the methanol synthesis. Although they showed higher selectivity for the reaction, they yield lower CO2 conversion. In this study, an ab-inito computational approach was utilized to understand the activity of Pd-ZrZnOx in comparison with the pristine-ZrZnOx catalyst for the methanol production. Unlike pristine-ZrZrO catalyst, Pd-doping was found to help the formation of more O vacancies on the surface of ZnZrO catalyst under methanol reaction conditions which are useful for CO2 conversion to methanol by increasing the number of active sites for the reaction. In the case of a high concentration of the vacancies on the surface, the formal charge on Pd could vary from 2+ to 0 depending on the reaction conditions. The charge variation on Pd also alters the hydrogen adsorption binding energies on the surface of the catalyst. For example, in the case of fewer vacancies on the surface when the charge on the Pd dopant was 2+, the hydrogen adsorption was calculated to be highly exothermic (-0.6 to -0.2 eV) on the surface oxygens in the proximity of Pd and Zn atoms. Whereas, for Pd with charge 0 (as shown in Figure), the hydrogen adsorption energies were calculated to be exothermic on Pd and Zn. In the same composition, H2 dissociatively adsorbed in a heterolytic fashion where Hδ- adsorbed on Pd and Hδ+ on surface oxygen. Such hydrogen atoms produced via heterolytic H2 dissociation are known to be an essential reactant in methanol synthesis via CO2 reduction.

Pd doping of Zn-Zr mixed oxide catalyst for CO2 hydrogenation to methanol

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.