Gold Nanoparticle Catalysts With Thermoregulated Self-separated Nature And Relevant Applications In Selective Oxidations Of Alcohol

Gold nanoparticle(GNP) catalysts have shown execellent catalytic performance in selective oxidations of alcohols, which become an advanced research hotspot. More recently, colloidal GNP catalysts as quasi-homogeneous catalysts have received wide attention. The GNP active sites in colloidal GNP catalysts can be accessed by substrates easily, consequently, such catalysts show high catalytic efficiency in liquid-phase selective oxidations. Generally, the stabilizers used in most colloidal GNP catalysts are organic compounds, which result in elevated difficulties in the separation and reuse of the catalysts. Cations/anions’ structure in task-specific ionic complexes(TSICs) can be easily tailored according to specific tasks, moreover, low surface tension of TSICs make them suitable for stabilizing nanoparticles. Thus, it is hopeful to solve the separation and reuse problems associated with colloidal GNP catalysts provided that TSICs are used as stabilizers.Based on previous research results, polyethylene glycol(PEG) chains were incorporated into TSICs in this thesis. According to the fact that PEG chains have apparent thermoregulated phase-transfer behavior in toluene, a series of colloid quasi-homogeneous GNP catalysts with unique thermoregulated self-separating nature were obtain and their catalytic performance in selective oxidations of alcohols was investigated. The main contents discussed were as follows:(1) A PEG6000 chain was incorporated into a TSIC containing vinyl and chloride ion, yielding [PEG6000VIM][Cl]. Then, the TSIC containing acetate anion, namely [PEG6000VIM][Ac] was obtained through anion exchange reaction. The two TSICs were used to stabilize GNPs, giving rise to corresponding GNP catalysts([PEG6000VIM][Cl]-GNPs, [PEG6000VIM][Ac]-GNPs). Using molecular oxygen as oxidant, the catalytic performance of the two catalysts obtained was investigated in alkali-free selective oxidations of benzyl alcohol. It was found that [PEG6000VIM][Ac]-GNPs possesses much higher turnover frequency(TOF) than [PEG6000VIM][Cl]-GNPs or the GNP catalysts reported in the literature in the same reaction. The catalyst of [PEG6000VIM] [AC]-GNPs-0.065 with Au content being 0.065 wt% was selected as optimum catalyst to investigate effects of solvent amount, reaction temperature, catalyst amount, and reaction time on the aerobic selective oxidations of benzyl alcohol. Under optimum reaction conditions, the catalyst show a TOF value as high as 0.63 mol·g-1·h-1.(2) In order to elevate conversion of benzyl alcohol, another metal was introduce into the catalyst of [PEG6000VIM][Ac]-GNPs, consequently, a series of bimetallic catalysts of(Au-Cu/[PEG6000VIM][Ac], Au-Ag/ [PEG6000VIM][Ac], Au-Mn/[PEG6000VIM][Ac], Au-Pd/[PEG6000VIM] [Ac]) were obtained, and Au-Pd/[PEG6000VIM][Ac] was demonstrated as the optimum catalyst. Then, Au/Pd content and structure was optimized, affording the best Au-Pd catalyst of Au1Pd7/[PEG6000VIM][Ac]-0.6 with molar ratio of Au to Pd being 1:7, and total metal content being 0.6 wt %. Under optimum reaction conditions, the catalyst showed a 98.3% conversion of benzyl alcohol with 99.0% selectivity to benzaldehyde.