A DFT Study Of The Mechanism Of Nanocarbon Catalyze For Acetylene Hydrochlorination Reaction

As one of the five major engineering plastics,the synthesis of PVC monomer vinyl chloride?VCM?is an important part of the production of PVC,in which the catalyst plays a vital role.For now,the mecury-based catalyst is dominated in the imdustry of VCM,the development and application of new mercury-free catalysts is imminent due to the severe mercury pollution caused by the high temperature volatilization of mercury and the trend of China's severe mercury resources and the trend of international mercury ban.Based on the theory of density functional theory,the mechanism of acetylene hydrogenation reaction on two nonmetallic carbon-based catalysts was studied by means of computational chemistry.The reaction mechanism of the C atom doping B₁₂N₁₂ cage?B11N12C,B12N11C?and three defective graphene?single vacancy graphene MVG,double vacancy graphene DVG and Stone-wales defect graphene SWDG?were explored to provide the experimental theoretical basis,to promote the development of low-cost and high stability non-metallic catalyst.The results show that the adsorption capacity of B11N12 C and B12N11 C on C2H2 and HCl is significantly enhanced compared with that of before doping,and C2H2 has two kinds of adsorption types on B11N12 C.The adsorption order of C2H2 is B12N11 C > B11N12C?trans?> B11N12 C,?cis?,the corresponding adsorption energy is-27.58,-25.87,-25.70;the adsorption order of HCl is B11N12 C,> B12N11 C,the adsorption energy is-3.06 and-1.58 kcal / mol.The analysises of the frontier molecular orbital theory?FMO?show that the electron aggregation in the frontier orbital of the doping site is favorable for the adsorption.The adsorption types of C2H2 on B11N12 C leads to the two reaction paths R1?trans?and R2?cis?,on B12N11 C is R3.The activation barrier of R1 is the lowest,36.08kcal/mol;R2 and R3 are 49.63 and 41.41kcal/mol,respectively.The rate control steps of the three paths are the dissociation of HCl molecules when the Co-ads transform into Ts state.The formation of defective sites in the defective graphene changed the uniform distribution of the surface of the graphene and allowed the electrons to accumulate near the defect sites,which obviously enhanced the interaction between the graphene and the reactants than the perfective graphene PG.DVG performed the strongest adsorption capacity for reactants than the other two defective graphene,and the order of adsorption energy is DVG> MVG> SWDG.The adsorption energies of C2H2 were-13.25,-6.22 and-1.92kcal/mol,respectively;the adsorption energies of HCl were-5.08,-4.43 and-3.28kcal/mol,respectively.The three defective graphene posess similar mechanisms,which the rate control step of the three paths are the dissociation of HCl molecules when the Co-ads transform into Ts state.The activation energies of MVG,DVG and SWDG are 39.46,41.55 and 41.16 kcal / mol,respectively,and the activation energy on MVG is the lowest,which was more favorable for the occurrence of hydrogenation of acetylene.