First-principles Studies On The Mechanisms Of C-H And C-O Bond Activations In On-surface Synthesis

In the field of organic synthesis,the activation of the C-H bond and the C-0 bond is one of the most crucial step in the production of long-chain chemicals.Due to the steady chemical properties of the C-H and C-0 bonds,the design of appropriate catalysts is required for achieveing the activations of the C-H and C-0 bonds.During this process,the metal surfaces not only serve as the support of the reactant but also exihibit catalytic activities for breaking the C-H and C-0 bonds.However,the reaction pathway and the underlying mechanism of the on-surface chemical reactions are difficult to observe directly via the traditional characterization method such as Scanning Tunneling Microscopy(STM).With the development of the computer technology and the Density Functional Theory(DFT),the reaction pathway and the catalytic mechanism of the on-surface synthesis can be simulated by theoretical approaches.In this thesis,the DFT calculations are performed to investigate the catalytic mechanism of the metal surfaces toward various on-surface synthesis.By employing the geometry optimizations,transition state searching and electronic structural analysis,two typical on-surface reactions are investigated in this thesis:C-H bond activations of the alkanes and the amidation reactions.Major contents are shown as follow:(1)The C-H bond activations on Au surfaces:the terminal C-H bond activations of the n-hexane(n-C6H-4)are selected as the model reaction to investigate the catalytic mechanism of the Au surfaces.By introducing the quantitative descriptors including the eftective d-band center and the effective d-band width.We propose that the catalytic activity of the Au surfaces is proportional to the effective d-band center and anti-proportional to the effective d-band width,in which the catalytic activity increases as the approach of the effective d-band center to the Fermi level and the decrease of the effective d-band width.In addition,we predict that the 2D Au-phthalocyanine(Au-Pc)surface may possess poor activity due to its low effective d-band center and the wide d-band width.(2)The propane dehydrogenations on the 2D Ru-Pc:by screening the potential catalytic performance of the 2D transition-metal Phthalocyanine(TM-Pc)frameworks,the 2D Ru-Pc framework exhibits the best catalytic activity and selectivity toward the propane dehydrogenation.The catalytic selectivity can be guaranteed by the weak propylene adsorption and the high over-dehydrogenation barriers.(3)The amidation reaction on the Au(111)surface:The reaction pathway of the amidation reaction is investigated by DFT calculations.With the assistance of the surface Au atom,the dehydrogenation of the amino group occurs firstly.The dissociated H atom further attacks the carboxyl group and achieves the dehydration.Finally,the coupling of the molecular radicals is achieved under the annealing.