Density Functional Theory Study Of Ni-Based Catalyst Catalyzed Acetylene Hydrogenation

Ethylene is one of the essential raw materials for the chemical industry and is vital for economic development.Currently,the presence of trace amounts of acetylene in the process of producing ethylene can further lead to the phenomenon of catalyst poisoning,and the common industrial method of acetylene removal is acetylene hydrogenation to ethylene.Pd-based catalysts for catalytic hydrogenation do improve the catalytic activity and efficiency,but noble metals as catalysts have more disadvantages,such as scarce resources,high price,high catalyst cost and harsh reaction conditions.Researchers are increasingly enthusiastic about the research of non-noble metal catalysts.Nickel metal is in the same group as palladium in the periodic table and has similar electronic properties,but the difference in price between the two makes nickel the superior choice to replace palladium.Nowadays,science and technology are changing rapidly,which help researchers to explore the pathway trends of catalytic hydrogenation and explain the mechanism of hydrogenation reaction in depth from the perspective of first principles.In order to solve the trace acetylene in the process and to improve the catalytic efficiency,the development of efficient catalysts adapted to acetylene catalytic hydrogenation is the most critical technology.In this thesis,the reaction mechanism of catalytic hydrogenation by three types of catalysts based on carbon materials is investigated sequentially by using a computational chemistry approach based on density functional theory（DFT）.Individual nickel atoms were doped into graphene-like BC₃ with P-atom modification,graphene-Ni Nx（x=1,2,3,4）non-noble metal catalysts doped with different numbers of N atoms,and g-C₃N₄,respectively.We explored the optimal reaction paths and the energy barriers of the reactions for different catalysts and performed a comprehensive analysis of their catalytic performance,which provided theoretical support and guidance for the catalytic acetylene Hydrogenation reaction with carbon materials.The results show that:（1）by comparing the reaction energy barriers of catalytic acetylene hydrogenation before and after P-atom doping,we found that the reaction paths of all three catalysts are two main processes:acetylene hydrogenation to ethylene and ethylene hydrogenation to ethane.For Ni-BC₃,the energy barrier for ethylene production is 13.55 kcal/mol with a selectivity of 3.63;for P-atom doped B site,the energy barrier for ethylene production is 18.12 kcal/mol with a selectivity of 12.71;for P-atom doped C site,the energy barrier for ethylene production is 16.29 kcal/mol with a selectivity of 2.06.Among them,the catalytic performance of P-atom doped B site was better compared to the other two catalysts.（2）In Graphene-Ni Nx（x=1,2,3,4）catalysts,graphene-Ni N₂ is divided into three stable structures,namely graphene-Ni N₂（A）,graphene-Ni N₂（B）,and graphene-Ni N₂（C）,according to the different arrangement of N atoms.Only one stable configuration exists for the remaining catalysts.It is shown by the adsorption energy values that the graphene-Ni Nx（x=1,2,3,4）catalysts all adsorb C₂H₂ molecules first and then H₂ molecules during the adsorption process,and then form a co-adsorption structure.In the reaction path of catalytic hydrogenation,a comparison of the energy barriers as well as selectivity of the six catalysts showed that Graphene-Ni N₄ had the best catalyst activity with an energy barrier of 25.24 kcal/mol for ethylene production and a selectivity of 26.35,which is a potential catalyst among the carbon and nitrogen materials for acetylene catalytic hydrogenation reaction.（3）The metal Ni atoms are preferentially adsorbed in the internal six cavities of g-C₃N₄,and the catalyst formed is Ni₁/g-C₃N₄,and the metal atom Ni is the only active site for the reaction.In the adsorption of reactants,the adsorption energy of C₂H₂ is greater than that of H₂,and C₂H₂adsorbs preferentially,thus forming a co-adsorption.By the reaction pathway study,the best reaction pathway is that of acetylene to ethylene and then to ethane.The energy bases were 20.05 kcal/mol and 90.29 kcal/mol,respectively,and the selectivity was 70.24.The Ni₁/g-C₃N₄ catalyst showed the best catalytic performance.