Abstract:
The stable performance of a Catalytic Dry Reforming of Methane (CDRM) catalyst is primarily determined by its ability to resist coke formation; in a broad sense, the coke formed on hydrogen production (i.e. methane dissociation) sites should be cleaned by mobile surface oxygen formed through CO2 dissociation. The experimental results suggest CO2 dissociation occurs on defect sites of zirconia when it is used as a catalyst support. In this study, it is aimed to understand the role of oxygen vacancy in activation and dissociation of CO2 molecule on m-ZrO2, which is a widely used CDRM support. For this purpose, DFT calculations were made to establish structure-reactivity relationships. Firstly, oxygen vacancy formation on m-ZrO2 (1̅11) surface was investigated, resulting structures and energetics were analyzed. It is found that presence of oxygen vacancies affects the surface in two ways: either zirconium atoms neighboring vacancy are reduced, or electrons are trapped at the vacancy and form localized states. In the second part of the study, CO2 adsorption onto stoichiometric and reduced m-ZrO2 (1̅11) surfaces were performed. The results revealed that the CO2 dissociation is thermodynamically favorable on reduced m-ZrO2 surface, and oxygen vacancies significantly lower adsorption energies and increase adsorbate-metal oxide interaction. Hence, it is shown that oxygen vacancies have a great influence on the dissociative adsorption of CO2 and zirconia has a clear potential as a catalyst support.
