A First-principles Investigation On Catalytic Performance Of Doped Low-dimensional Carbon Nanostructures

In recent years, low-dimensional carbon nanostructures such as graphene oxide, graphene and carbon nanotube have shown potential applications in many areas. The investigation on special features of these nanostructures has been the hot topics in the fields of chemistry, physics, biology and material science for a long time. Considerable efforts has been drawn to investigate the structural, physical and chemical properties for these nanostrucctures to develop new applications. In this dissertation, we discussed the structures, adsorption and catalytic performance of a bunch of low-dimensional carbon nanostructures derived from graphene, including graphene oxide, Pt-doped graphene oxide, transition metal-doped graphene and carbon nanotubes, summarized as the following:Firstly, we investigated the formation and evolution of defects on graphene oxide with first-principles-based thermodynamics. Graphene and reduced graphene oxide have long been considered as support materials for transition metal catalysts. However, their applications are limited due to the weak transition metal-graphene interfacial interaction, which can not stablelize the transition metal nanoparticles effectively. Defects have been shown to interact strongly with the transition metal nanoparticles which provides a feasible way for the fabrication of stable, durable and efficient graphene-supported transition metal nanoparticles. The results shows that the formation of defects is a spontaneous process in oxidative environments and requires less critical conditions than those for the completely oxidized graphene. We also showed that the stability of these defect structures depends on the ways how the carbon atoms around the vacancy are passivated. In oxygen-poor condition, the size of vacancy is by the diffusion of oxygen-containing groups.Then, we investigated the reduction and formation of defects on graphene oxide assisted by the deposited Pt atoms. The reduction of graphene oxide is important for graphene oxide modification and preparation of graphene. We showed that the diffusion of oxygen-containing groups and the interaction between H2and graphene oxide can be modified by the deposited Pt atoms. These Pt atoms activate H2and play a key role in reduction. Furthermore, C atoms can be replaced by Pt atoms and generates carboxyl and Pt doped graphene oxide. Alternatively, Pt doped graphene can be also formed by the diffusion of Pt atom to the defects passivated by epoxyl and carbonyl on reduced graphene oxide. After that, we investigated the structural and electronic properties of transition metal (from V to Zn) doped graphene and their reactivity to O2, O, CO and NO adsorption. Due to the strong interaction between transition metal atoms and defect graphene, these transition metal atoms can be effectively stablized. has shown to be effective catalysts in heterogeneous catalytic reaction. The reactivity of these transition metal doped graphene to O2, O, CO and NO adsorption can be correlated to the averaged weight center of the transition metal d-states.Finally, we studied the CO oxidation over Pt and Fe doped graphene, and the potential promotion effect of heteratom modification and local curvature. We showed that the CO oxidation follows Langmuir-Hinshelwood mechanism over Pt-doped graphene, but follows Eley-Rideal mechanism over Fe-doped graphene. We also showed that further modification of Pt-doped graphene with N will promote the reaction kinetic according to the lower activation energies. Similar trend was observed over Fe-doped graphene. The local curvature on graphene will also tune the activation barrier for CO oxidation and a promotion effect was found on the concave surface of Pt-doped graphene.