The Oxidation Of Ethylene And Vinyl Chloride On Different Metal Catalyst: A DFT Study

In this thesis, the decomposition mechanisms of methylamine and methane on some catalysts surfaces have been systematically investigated by DFT-GGA method and slab model. The reactivity difference of various catalysts surfaces has been studied by the calculation of activation energy. The main conclusions of this work are summarized as follow(1) This work represents a systematical theoretical study of ethylene epoxidation on different metals by the DFT-GGA calculations, and we draw some important conclusions such as:On metal surface, the order of adsorption energy of possible species such as atomic oxygen and OMME increases as that of both the activation energies of epoxide formation and acetaldehyde formation from OMME (Ag< Pt< Rh< Mo); the reaction selectivity for the EtO formation on Ag (111) is higher than that on other metals, which means that the strongly adsorbed OMME is not correlated with its high selectivity; It is found that the closer of the TSs to the reactant, the more activity for the epoxidation of ethylene on metal surface will be. The order of OMME adsorption energy can be explained by the PDOS of molecular OMME, i.e.; the lower the HOMO energy of molecular OMME, the larger of OMME adsorption energy. (2) The work represents a systematical theoretical study of ethylene epoxidation on Ag2O(111). Cu2O(111) and Au2O(111) metals by the DFT-GGA calculations, and we draw some important conclusions such as:A good linear correlation is not found between the active energy and the adsorption energy of OMME on different surface. The active energy is lowest of react on Ag2O(111),but the selective of EO is not high. On Cu2O(111), The active energy is higher, the selective of EO is more than 50%. The active energy is highest of all researched systerm, the slective situation on Au2O(111) is similar to Ag2O(111).(3) The work represents a systematical theoretical study of ethylene epoxidation on Pt(111),Pt/Ag-2(111),Pt/Ag-4(111) and Ag(l 11) metals by the DFT-GGA calculations, the results after calculation are good agreement with the conclusions of experiment. The results show that the reaction mechanism is a two-step process:first forming OMME and then the products. We also draw some important conclusions such as:instead of a good linear correlation, a parabola correlation is found between the active energy and the adsorption energy of OMME on different surfaces, the activity energy is the lowest when the reaction is processing on Pt/Ag-4(111) surface.(4) The work represents a systematical theoretical study of vinyl chloride epoxidation on different metals, and some important conclusions are as the followings:owing to the asymmetry of vinyl chloride, there are three intermediates(OMMC(1).OMMC(2) and OMMC(3)) in the reaction of vinyl chloride epoxidation. The reaction pathway of vinyl chloride via OMMC(3) is more favoured than any others; the activation energies of reactions from OMMC(3) to products are in the order of Ag< Pt< Rh, however, the reaction selectivity on Ag (111) is lower than that on Pt(111) and Rh (111); the order of the stability of OMMC(3) on different is obtained by analyze the metal atom d-band center position, and the order is the same with that of the activation energies of vinyl chloride epoxidation. Namely, the more stable of OMMC intermediate, the higher of the correlative activation energy is.