Application Of Gold Nanoparticle-H₂O₂ Catalytic System In Epoxidation Of Olefins

Supported gold nanoparticles (GNPs) are a new kind of catalytic materials, which have been demonstrated to be very promising catalysts in many important industrial processes and environmental protection fields, such as low-temperature CO oxidation, selective oxidation of alcohols or aldehydes, epoxidation of olefins, catalytic combustion of hydrocarbons, oxidative decomposition of halogenated organic compounds, removal of NOx, etc. In this dissertation, a series of periodic mesoporous organosilica (PMO) materials incorporating disulfide-ionic liquid moieties and a NH2-containing ionic liquid polymer were prepared and used as support for fabricating supported GNP catalysts. Catalytic performance of the resultant catalysts was investigated in epoxidation of olefins. The main contents discussed were as follows:(1) An organic bridged silsesquioxane precursor containing disulfide-ionic liquid moieties was synthesized and co-condensed with tetraethoxysilane or sodium silicate in the presence of different templates, leading to three PMO materials with various pore architectures. GNPs, derived from in-situ reduction of aqueous chloroaurate ions by the silanols located on the pore surface of the PMO materials, were captured by sulfide groups, giving rise to relative GNP/PMO composite catalysts. In a series of epoxidation reactions of various olefins, the three GNP/PMO composite catalysts showed different catalytic performance. In general, the catalysts with 1-D pore architecture revealed better catalytic performance than the catalysts with 3-D pore architecture, meanwhile, the larger pore size in the catalysts with 1-D pore architecture, the better catalytic performance. It should be noted that the three GNP/PMO composite catalysts possess rather excellent reusability; they could be reused for 10 times without significant loss of catalytic activity.(2) The above-stated organic bridged silsesquioxane precursor was grafted onto siliceous SBA-15 via a post-synthesis procedure. The resultant PMO material was employed for fabricating GNP/PMO composite catalyst via a process involving in-situ reduction of aqueous chloroaurate ions by the silanols located on the pore surface and successive capture of the formed GNPs by sulfide groups. The obtained GNP/PMO composite catalyst was well characterized by means of N2 adsorption-desorption, TEM, EDX-mapping,29Si MAS-NMR, FT-IR and UV-Vis. Using epoxidation of a-pinene as test reaction, the effects of reaction time, reaction temperature, oxidant amount and catalyst amount on catalytic performance of the GNP/PMO composite catalyst were investigated systemically. Under optimum conditions, the conversion of a-pinene and the selectivity toα-pinene epoxide were as high as 81.8% and 94.9%, respectively; moreover, the catalyst could be reused for 6 times without significant loss of catalytic activity.(3) An amino-functionalized ionic liquid of N-(3-aminopropyl), N(3)-(vinyl)-imidazolium bromide (AIL) was synthesized and used to stabilize gold nanoparticles (GNPs). Further polymerization of the resultant GNP-containing AIL led to a composite catalyst with GNPs being supported by ionic copolymer (GNPs-P-AIL). The obtained composite catalyst was characterized by means of FT-IR, UV-Vis, and TEM. It was found that GNPs-P-AIL remained the structure of ionic liquid moieties in the parent AIL after GNPs loading and successive polymerization processes and that GNPs in the composite catalyst dispersed uniformly with the particle size of 6-8 nm. GNPs-P-AIL showed good catalytic performance in the epoxidation of styrene using H2O2 as the oxidant. The conversion of styrene and the selectivity for styrene oxide were as high as 81.5% and 88.3%, respectively, when the reaction was performed at 60℃for 6 h.