AB initio modelling of materials proper ties for catalytic and device applications

Şensoy, Mehmet Gökhan
The first-principles computations based on density functional theory is used to study the adsorption properties and the activation of CO, CO2 and H2O on gamma-Al2O3(100) surface. A systematic study has been conducted to identify the most stable adsorption sites for both mono- and di-atomic Pt clusters. Several stable adsorption geometries have been identified for the species as well as introduces their interaction with Pt clusters and the support. In this context, analysis of the adsorption properties allows us to establish the most stable configuration in a reaction mechanism. Another important factor in the reactivity of catalyst is the support material which has a great influence on the efficiency and activity of a catalytic reaction. Transition metal carbides (TMCs) are a good alternative as a support material in a catalytic reaction. Therefore, studying on the surfaces of platinum carbide (PtC) as a support material is being important. While the bulk structure of zincblende (ZB) PtC has been investigated several times, a detailed understanding of the electronic and structural properties of its low-index surfaces is lacking. Within this study, we present an ab-initio investigation of the properties of five crystallographic ZB PtC surfaces, Pt/C-terminated PtC(100), PtC(110) and Pt/C-terminated PtC(111). Adsorption geometries have been identified for the atomic oxygen, and its interaction with surface atoms is characterized in terms of adsorption energies and the nature of bonding between the adsorbed and surface atoms. Calculated vacancy formation energies indicate facile C removal (exothermic) on the ZB PtC(111) surface, and Pt-vacancy formation is endothermic with respect to the vacancy formation energy. An ab-initio thermodynamical analysis shows that the most stable surfaces are the Pt-terminated PtC(100) and PtC(111) surfaces, and the higher oxygen coverages of PtC(100) surface are stable even at temperature as high as 3000 K. In addition to the catalytic properties of an oxide surface and TMCs, we have also studied the interaction of chlorine (Cl) atom with graphene sheet and H-terminated graphene nanoribbons (GNRs) based on density functional theory (DFT). We have discussed the electronic and structural properties of adsorbed Cl atom on pristine and defective graphene under applied electric field. We have found that the most stable adsorption configurations are the on-site geometry and hollow site aligned parallel to the graphene plane for single and molecular Cl atom (Cl2), respectively. The energy band structures are also performed to understand the nature of size effect including the effects on the magnetization, adsorption behavior of single Cl atom and charge transfer in graphene nanoribbons with zig-zag and armchair edges. 
Citation Formats
M. G. Şensoy, “AB initio modelling of materials proper ties for catalytic and device applications,” Ph.D. - Doctoral Program, Middle East Technical University, 2017.