Multiscale Simulation Of The C-H Bond Activation Of Several Hydrocarbons

The products of C-H bond activation are important chemical raw materials.To meet its growing demand,expanding production capacity and optimizing catalysts have important economic value and scientific significance.In order to shift from the traditional trial-and-error catalyst development process to rational design,it is necessary to understand the reaction mechanism,structure-activity relationship of the catalyst,role of different active sites,etc.In this thesis,C-H bond activation on pure metal,supported metal catalyst and nanocarbon catalyst are studied through multiscale methods such as first-principles calculation and micro-kinetic simulation.The following discussions were held:(1)The process of propane direct dehydrogenation on Pt(111)was simulated.Spatially resolved kinetic Monte Carlo simulations were used to obtain the evolution of the reaction process and the adsorption state of the catalyst surface.Through first-principle calculation,the detailed reaction network of propane dehydrogenation was explored.The energy barrier of each elementary reaction was obtained.The reaction process and the evolution of the adsorption state of the catalyst surface were obtained,and two stages of reaction observed in experiment was reproduced.Through the flux analysis,the mechanism of the reaction and the origin of the coke precursor are revealed.Further,the reasons for the two stages were explored by comparing the surface adsorption state with the calculated macroscopic properties(such as reaction rate,selectivity,etc.),and the effect of coke precursor on the configuration of free site was revealed.In addition,by changing the proportion of hydrogen in the reaction atmosphere,the influence of hydrogen on the reaction was revealed.This study lays out a solid base for the future optimization of the Pt catalysts in PDH and we propose that the fine control of the surface sites on Pt has paramount importance to reduce the coke formation.(2)By constructing a metal oxide CeO2 supported Ni catalyst model,the support effect on the stability of the catalyst in the dry reforming of methane was explored.The global optimization algorithm was used to optimize the configuration of the supported Ni particles.Five types of active sites were considered:metal surface,support surface,interface of metal and support,oxygen vacancy on suppor surface,and oxygen vacancy at the interface.The calculations of the methane dehydrogenation and the carbon dioxide activation process were performed on these five types of site.The energy calculation and electronic structure analysis of coke elimination reaction were further carried out.The possible path of carbon deposition elimination and the possible origin of the high stability of the catalyst are proposed.An updated reaction mechanism is proposed to explain the high stability.This work not only deepens the understanding of catalytic properties of supported Ni catalysts in DRM but also signifies the effectiveness of interface engineering for the improvements of catalytic performance.(3)The complex reaction mechanism of ethylbenzene oxidative dehydrogenation on nanocarbon catalysts was simulated by first-principles calculation based micro-kinetic modeling.Four possible mechanisms were studied which are Eley-Rideal(ER),Langmuir-Hinshelwood(LH),and Mars-van Krevelen(MvK)respectively together with the reactions between weakly adsorbed species and radicals.Furthermore,through micro-kinetic modeling,the most possible reaction mechanism under different reaction conditions and the contribution of each path to the reaction rate were explored.The reaction order is determined through the relationship between rate and partial pressure of the reactants.In addition,by changing the initial defect site concentration,the transformation of defects in the reaction process and its influence on the reaction were explored.This study provides a decisive description of mechanism of ODH on nanocarbon catalysts under various reaction conditions and sheds light on design of catalyst and optimization of reaction conditions.