Theoretical Studies For Graphene Oxide And Vacany Graphene Supported Transition Metal

Due to unique mechanical, optical and electronic proterties, graphene has stimulated a wave of research boom. However, external oxygen-containing groups or defect will remain graphene surface during the production process. On the one hand, oxygen-containing functional groups or defects can undermine the integrity of graphene, on the other hand, these will give graphene special properties. Foreign metal atoms can combine with the oxygen-containing functional groups or defects and make as various catalysts. In this thesis, we performed density-functional calculations combined with periodic slab model to investigate the catalysis property of graphene oxide or vacancy graphene supported transition metal. The main contents are as following:1. The bonding behavior of hydroxyl and epoxy groups on the graphene surface was investigated. The calculated results suggested that two oxygen-containing groups always tended to bind with the neighboring carbon atoms at the opposite sides. Moreover, multiply hydroxyl groups tend to aggregate on the graphene platelet in the form of armchair or zigzag configuration. Density of states showed that different number of hydroxyl groups induced different electronic properties. The energy band gap not only depended on the number of oxygen-containing groups but also depended on the arrangement of oxygen-containing groups.2. We compared the stability and electronic structure of Pdn (n=1～5) clusters on isolated system and single vacancy graphene surface, and adsorption of an oxygen molecule on such clusters were studied in detail. The results show that the point defect acts as a strong binding trap for Pd clusters and is favorable for the dispersion of Pd nanoparticles. The existence of graphene support promotes the adsorption of O2 molecule, and further makes the O-O bond elongation.3. The catalytic oxidation of CO on Pd-anchored graphene and Pd-embedded graphene (Pd-GO and Pd-VG) were investigated, respectively. The results validate that both Pd-GO and Pd-VG show good catalytic performance for CO oxidation. Moreover, the lower reaction energy barrier makes Pd-VG system slightly superior than Pd-GO system in catalytic performance. The reaction proceeds via Langmuir-Hinshelwood mechanism with a two-step route (CO + O2 â†' OOCO â†' CO2+O), followed by the Eley-Rideal mechanism (CO+Oâ†' CO2).4. Density functional theory calculations have been performed to investigate the NO reduction on Cr-embedded graphene (Cr-VG) via direct dissociation mechanism and the dimer mechanism. The results show that no matter the direct dissociation mechanism or the dimer mechanism, the dissociation energy is least when NO is adsorbed on Cr-VG with O-end mode. The dissociation energy are 0.85 eV and 0.35 eV, respectively. Therefore, the O-end mode is favorable for NO dissociation, while it is unfavorable for NO dissociation with N-end mode.