The Reaction Mechanism Of Acetylene Hydrochlorination Over Au-based Catalysts

In this paper, the non-mercury catalytic reaction system of vinyl chlorideproduced by the method of acetylene was chosen as our study object. The reactionmechanism of AuCl₃catalyst, which was a representative non-mercury catalyst, wasstudied using the density function theory （DFT）. The deactivation reason of AuCl₃catalyst was discussed and some further researches were carried out to improve thecatalytic property of Au-based catalyst. The conclusion from this study will shed lighton the experimental design of novel non-mercury catalysts with high performanceThe calculation results showed that the acetylene hydrochlorination reaction withAuCl₃catalyst would happen through two paths. In one path （denoted as path1）, C₂H₂and HCl were co-adsorbed on the Au catalyst to react and form the vinyl chloride. Atfirst, the Ï€-σ coordination structure was formed by the interaction between the AuCl₃catalyst and C₂H₂, and the C₂H₂was activated. The chlorovinyl, which adsorbed onthe catalyst, was formed by the reaction of the C₂H₂and adsorbed HCl. The adsorbedchlorovinyl could reaction with another adsorbed HCl to produce vinyl chloride. Thisprocess needed an activation free energy of97.60kJ/mol. If the HCl could not besupplied timely, the active site of Au catalyst would be covered and the catalyticactivity would decrease. In the other path （denoted as path2）, a side reaction would beoccurred via the C₂H₂adsorbed on the catalyst alone when HCl is not sufficientaround the catalyst, with forming the by-product of dichloroethylene. The AuCl₃catalyst was deactivation due to the structure destroyed and reduction of Au³⁺.A surplus electron in the system of Au catalyst would effectively improve theinteraction between catalyst and HCl, which could guarantee the main reaction carryout smoothly, and the active site was released rapidly. More importantly, the sidereaction was suppressed. As a result of that, the catalytic life of Au-based catalyst wasextended. When the active carbon support was doped with N, the interaction betweenAu catalyst and the support was increased, Which improved the stability of catalyst.The doped N could promote the polarization of the Au-Cl bond, inducing theinteraction between AuCl₃and HCl increased.