Study On Low Au Loading Of Au/CoCeO₂-AC Bifunctional Catalyst For Acetylene Hydrochlorination

Polyvinyl chloride(PVC)is an important engineering plastic obtained from the polymerization of vinyl chloride monomer(vVCM).The production of VCM with acetylene hydrochlorination technology took market share over 80%in China,but the mercury catalyst used in this method is subject to be restricted due to pollution problems.It is particularly urgent to develop alternatives to the mercury catalyst.Studies have shown that activated carbon loading Au(Au/AC)is more likely to replace the mercury catalysts.However,due to the fact that gold catalysts are easily to be deactivated and high cost issues,their industrial applications are limited.This dissertation aims at the system of VCM by acetylene hydrochlorination and focuses on the fabrication of a bifunctional Au/CoCeO2-AC bifunctional catalyst with low Au loading.More attention is paid on the deep exploration of structure-activity correlation of the catalyst,in order to provide the basis of creating a new catalyst for the VCM production by acetylene hydrochlorination.Based on the previous work,this dissertation developed a bifunctional catalyst with ultra-low Au loading.A typical Au/CoCeO2-AC bifunctional catalyst is prepared by mechanically mixing AC with Au/CoCeO2 which Au loading on the CoCeO2 carrier surface by deposition-precipitation method.The preparation of catalyst avoids using aqua regia as solvent to disperse Au nanoparticles,which makes the preparation process more environmentally friendly.The results indicate that the bifuanctional catalyst with 0.1 wt%Au loading shows the highest atomic economy by comparing the TOF values of different Au-based catalysts.Therefore,it is used as a benchmark for further study.The structure,physico-chemistry property and catalytic mechanism of Au/CoCeO2-AC bifunctional catalyst are characterized by XRD,XRF,Raman,TEM,H2-TPR,XPS,and HCl/C2H2-TPD.The characterization results show that highly dispersed Au nanoparticles/clusters are evidenced on the surfaces of CoCeO2 carrier.The solid solution formed by Co3O4 and CeO2 promotes the adsorption of HCl.During the activation phase,more Au3+ species are generated on the surface of Au/CoCeO2 which can activate HCl to promote the reaction,while the function of AC is the strong adsorption capacity of C2H2.The mechanical mixing of Au/CoCeO2 and AC can produce a bifunctional synergistic effect between the two moieties,as inhibiting acetylene over coating the surface of Au?+(? = 1,3)active site and thus retarding the catalyst deactivation.Thus,the bifunctional synergistic effect can maintain the content of Auiu and exhibit excellent acetylene hydrochlorination activity and catalytic stability.Under the reaction condition of:T= 180 ?,P = 0.1 MPa,V[HC1/C2H2]= 1.2 and GHSV[C2H2]= 180 h-1,the initial acetylene conversion was 89%over the bifunctional catalyst of Au/CeO2-AC,and the conversion:rate increased to 93%over the bifunactional catalyst of Au/CoCeO2-AC.Under this condition,the acetylene conversion on Au/CoCeO2-AC bifunactional catalyst maintained more than 90%for 30 h,while the conversion on Au/CeO2-AC bifunactional catalyst decreased to 82%.The finding indicates that the introduction of Co in CeO2 carrier can further improve the activity of the bifunctional catalyst and the bifunctional catalyst has industrial application potential.