Study Micro-Mechanism Of CH₄Dissociation On Metal Surfaces

plays an important role in chemical industry. More importantly, it is very meaningful to clarify the mechanism of CH4dissociation on catalysts in the development and application. A large number of studies are focus on the dissociation of CH4on metal surfaces, especially, on transition metal (VIII) surfaces.In recent years, with the rapid development of computation level and calculation method, the quantum chemistry calculation has been widely used to investigate the transition metal for catalytic reaction systems. In this dissertation, by using the first principle density functional theory methods together with the periodic slab model, we firstly report the adsorption and dissociation of CH4on metal Rh, Pt and Co surfaces, further, the CH spillover on Rh-Cu bimetallic surface via three different spillover processes are discussed in detail.In this dissertation, we have studied the CH4dissociation on Rh(hkl), Pt(hkl) and Co(hkl) surfaces, on the basis of energy analysis, the preferred adsorption sites of CHx(x=0-4) and H species are located, then, the stable co-adsorption configurations of CHx(x=0-3)/H are obtained. Further, based on the results of thermodynamics and kinetics, the dissociation mechanism of CH4 on Rh(hkl), Pt(hkl) and Co(hkl) surfaces show that on Rh(111) and Rh(100) surfaces, CH is the most abundant species, on Rh(110) surface, CH2is the most abundant species, meanwhile, CH4dissociation on Rh(100) surface is the most preferable reaction surface; then, on Pt(111), Pt(110) and Pt(100) surfaces, CH is the most abundant species, meanwhile, CH4dissociation on Pt(110) surface is the most preferable reaction surface; moreover, on Co(111) surface, CH is the most abundant species, on Co(110) surface, CH3is the most abundant species, on Co(100) surface, C is the most abundant species, CH4dissociation on Co(100) surface is the most preferable reaction surface. Above calculated results suggest that the activity order of CH4dissociation on metal Rh, Pt and Co surfaces is as follows:Rh> Pt> Co.We also have calculated the CH spillover on the Rh-Cu bimetallic surface via three kinds of ways, such as, direct spillover, H-assisted spillover and H2-assisted spillover, respectively. In all spillover processes, CH can spillover from Rh surface to Rh-Cu interface, but CH can not spillover from Rh-Cu interface to Cu surface. Meanwhile, for CH spillover from Rh surface to Rh-Cu interface only need to overcome a low activation energy of75.4,85.4and76.0kJ·mol-1, respectively. These results show that Rh-Cu bimetallic catalyst can effectively reduce the activation energy of CH4dissociation in comparision with that on Cu.