| Data revealed that China contributes to about 10% of the global annual consumption of mercury, and 60% of that is used as catalysts for acetylene hydrochlorination. Along with the increasing environmental concerns, prohibition of mercury based catalysts is inevitable. Thus, searching of greener and efficient alternatives appeared to be imminent. Intensive investigations proved Au based catalysts to be extremely active towards acetylene hydrochlorination reaction. However, due to the high cost of gold, Au catalysts are much more expensive, thus further enhancement on its catalytic efficiency (stability and activity) is always necessary. There are many work focusing on this topic. Notwithstanding, lacking theoretical guidance has blocked the investigations, and previously reported Au catalysts are not efficient enough for application.Based on in-depth understanding of gold catalysts, we discussed the effects of support and preparation method on the final catalytic performance in this thesis. Besides, systemic investigations on active sites were also carried out. Major conclusions of this article are listed below:1) SiO2/C composite support was investigated and used as support for gold catalysts. The preparation procedure of catalyst and content of SiO2 was detailed optimized. The optimized catalyst, 1Au/5SiO2/AC1, showed improved stability in acetylene hydrochlorination reaction. Silica deposition brought down surface area of the catalyst while led to better distribution of gold nanoparticles (Au NPs). Higher level of resistance to acetylene, excellent surface property stability and less carbonaceous deposition were determined as the origin of improved stability of lAu/5SiO2/AC1.2) A new and efficient impregnation method involving mixture solvents and vacuum drying process was used to prepare gold catalyst (MIV-1Au/C1) for acetylene hydrochlorination reaction, which brought about 94.3% higher catalytic activity than the traditional method (PI-1Au/C1). The MIV method was green, mild and simple. Moreover, it appeared to be controllable by tuning some preparation parameters, which is an incomparable advantage. It was demonstrated that Au in MIV-1Au/C1 presented as FCC Au0, which was determined to be the only active species at the beginning/highest point of the testing. Much better Au dispersion was observed in MIV-1Au/C1. In comparison with dominating single crystals in PI-lAu/Cl, AuNPs in MIV-1Au/Cl appeared to be multiple twinned particles, poly crystallines or incomplete particles, all of which could provide plenty of active sites for acetylene hydrochlorination. Moreover, these Au NPs in MIV-1Au/C1 could be re-dispersed more easily by HCl and C2H2 than those in PI-1Au/C1, which was associated with their strained structures.3) Using molecular simulation, ability of three reported active sites, namely AuCl3, AuCl and AuCN, in activating acetylene was studied theoretically at the level of density functional theory (DFT). Energy decomposition analysis (EDA) and natural population analysis (NPA) were also applied to scrutinize the interaction of gold complexes and C2H2. The results demonstrated that Au+ compound could activate C2H2 more efficiently than Au3+; Besides, this effect could be deeply influenced by the ligand of Au+, while electron-drawing ligand, like CN-, was not preferred in activating C2H2. Further calculation revealed that AuI could also activate C≡C efficiently, and the interaction energy between Aul and C2H2 was mild whilst AuI being stable. Experimental results proved that the activity and stability of the low cost 0.1AuI(KI)/AC2 exceeded those of all previously reported gold catalysts for acetylene hydrochlorination. This result authenticated the reliability of theoretical calculations. Long term testing showed that 0.1AuI(KI)/AC2 was five times more stable than commercialized mercury based catalyst. The production of VCM over 0.1AuI(KI)/AC2 reached 71% of the industrial catalyst in 290 h, firmly suggesting its potentiality in industrial applications.4) Influence of preparation and treatment parameters on induction period of 0.1AuI(KI)/AC2 was studied. It was finally determined that calcination temperature was essential in facilitating coordinative unsaturation while and some gases (N2, H2O and HCl) could protect these sites, and finally combed-out the induction period. According to the experimental results, if 0.1AuI(KI)/AC2 was calcined in water vapor (pure water or trace water in N2) for 3 h at 240 ℃, the induction period could be thoroughly eliminated. Besides, it was also found that moisture content of the support has negative effect on elimination of induction period. |
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