Study On Catalytic Mechanism Of Au-based Catalyst Interface Phenomenon For Acetylene Hydrochlorination Reaction

Polyvinyl chloride(PVC) is one of the world’s three general resin materials, which is produced from the polymerization of vinyl chloride monomer(VCM). According to the Chinese energy structure, the industrial production of VCM is mainly through the reaction of acetylene and hydrogen chloride. In the process of industrial production, the reaction is catalyzed by mercuric chloride catalyst. But the mercuric chloride catalyst is heating volatile after the reaction, which will make the catalyst deactivation and damage the human health causing environmental pollution. Therefore, in order to achieve the green sustainable development strategy, investigation the environment friendly and high efficiency non-mercury catalyst for acetylene hydrochlorination is necessary.Based on pioneering work and systematic studies, the researchers found that the correlation of activity of metal chlorides supported on carbon for acetylene hydrochlorination with the standard reduction potential, and considered that the Au-based catalyst exhibits an excellent conversion of acetylene and selectivity of vinyl chloride for acetylene hydrochlorination, but the active component of Au3+ has a poor stability in the reaction. The reason of deactivation is assigned that the active component of Au3+ was reduced to metallic Au and the deposition of carbonaceous. At present, the stability of the Au-based catalyst is the main problem that restricts the application of gold catalyst in the process of acetylene PVC. In this paper, the interfacial interaction between Au catalyst and co-catalyst and carbon support was studied systematically, put forward the effective method to improve the stability of the gold catalyst, provide a reference for the industrial application of gold catalyst.The main content divided into the following sections:(1) Adding the other metal into the Au nano-particles as the active component, the influence of interface effect on the catalytic performance of acetylene hydrochlorination reaction was investigated. The result showed that in the activity test of hydrochlorination reaction, the conversion of acetylene was not significantly improved. The addition of second groups of metals did not make the interaction between the gold and the transition metals, which displayed that the interface was not formed. By adding the auxiliary catalyst, the stability of the reaction has decreased.(2) We synthesized a novel non-mercuric catalyst with AuCl3 and thiourea as precursors, and active carbon(AC) as a support, the interface was formed between the metal cation and the anion thiourea, the synthesized AuCl3–thiourea/AC catalyst was applied to acetylene hydrochlorination. After adding the thiourea, the conversion of acetylene has a significantly improved, and the AuCl3–thiourea/AC catalyst containing 0.4 wt% Au exhibited a similar catalytic performance to the AuCl3/AC catalyst containing 1 wt% Au. The temperature-programmed reduction(TPR) experiment was test to determine the addition of thiourea as a ligand can affect the valence of Au in the preparation process of the catalyst. Transmission electron microscope characterization and X-ray diffraction display that the addition of thiourea promoted the dispersion of the gold species during the preparation. X-ray photoelectron spectroscopy(XPS) was systematically employed to research the relationship between the Au species and thiourea, the catalyst with thiourea added to promote the oxidation of Au0 to Au+ and Au3+. The Au+ species as the active component and improved the conversion of acetylene. The temperature program decomposition(TPD) experiments to determine the interactions between Au and thiourea, based on the adsorption strength of hydrogen chloride. The presence of more Au3+ and Au+ active sites in the catalyst may enhance the adsorption of hydrogen chloride, and thus promote its catalytic activity.(3)Preparing the hollow carbon spheres(HCS) as the support, Au nano-particles as the active component, the interface was formed between the metallic and the carbon, the synthesized Au/HCS catalyst was applied to acetylene hydrochlorination. The result of TEM indicated that the HCS was synthesized and the material had obvious hollow structure. The Au nanoparticles were uniformly dispersed and not agglomerated on the surface of HCS. The catalyst was applied to the acetylene hydrochlorination reaction displaying an excellent catalytic activity.