Experimental and computational study of selective co oxidation over Au/Al2O3 catalyst

Abstract

This study objects the experimental and computational investigation of preferential oxidation of carbon monoxide over Al2O3 supported gold catalysts. In the experimental part of the study, reaction kinetics of CO oxidation was studied both in the presence and absence of H2, CO2, and H2O. Our results demonstrated that the reaction proceeded through a two-step Eley-Rideal-type mechanism involving the formation and decomposition of the reaction intermediate (OO-CO) on the perimeter interface of Au and support. In the presence of H2, CO2, and H2O; on the other hand, the mechanisms involving both the adsorption and dissociation of O2 became significant, as well. In the computational part of the study, the reaction was modeled using density functional theory method in order to provide a molecular level understanding of the findings obtained in the experimental part. CO oxidation was first model over a gas phase Au6- cluster in the absence of hydrogen. Due to the small size of the considered model, co-adsorption of the reactants was possible on the selected cluster and the reaction was found to proceed through a two-step Langmuir-Hinshelwood-type mechanism. For the investigation of hydrogen on the reaction mechanism, a cubooctahedral Au13 cluster was employed and it was observed that the effect of H was limited to holding the reactants together and facilitating the O2 activation rather than causing a decrease in the reaction barriers of the corresponding steps. The theoretical part also involved the investigation of a structure and activity relationship for CO and O2 adsorption over gold nanoparticles in order to determine the effects of various parameters on the catalytic activity of gold clusters. Accordingly, charge was found to be the most significant parameter in determining the CO adsorption energy, whereas unpaired electron was the most significant one in determining the O2 adsorption.