Constructing Catalytically Active Oxidation Center Of Gold Nanoparticles In Mesoporous Organic-inorganic Interpenetrating Networks

Supported gold nanoparticle(GNP)catalyst is a new kind of catalytic material,which has been demonstrated to be very promising catalysts in many important selective oxidations,such as low-temperature CO oxidation,selective oxidation of alcohols or aldehydes,epoxidation of olefins,oxidation of alkanes,and direct oxidation of hydrogen to hydrogen peroxide.It has been reported that the catalytic performance of supported GNP catalysts is strongly dependent on the particle size of GNPs.GNPs have high surface energy and low melt point,and would be vulnerable to aggregation in the absence of space confinement,leading to rapid deactivation.In this context,the selection and design of supports would be critical when preparing supported GNP catalysts.In this dissertation,a series of mesoporous organic-inorganic interpenetrating network materials were synthesized and used as supports for fabrication of supported GNP catalysts through in situ reduction of chloroaurate ions by the surface silanols of the mesoporous hybrids.Successively,the catalytic performance of the resultant catalysts was investigated in H2O2-mediated styrene epoxidation.The main contents discussed were as follows:Preparation of a series of mesoporous organic-inorganic interpenetrating network materials was achieved via a one-pot process involving self-assembly of melamine-thiourea-formaldehyde with aqueous silicate in the presence of P123.Using the resultant mesoporous hybrids as supports,relevant supported GNP catalysts were obtained via a synergistic capture-reduction process involving capture of HAuCl4 by N and S in the organic network and successive reduction by silanols in the inorganic networks.The obtained supported GNP catalysts were characterized by XRD,N2 sorption,TEM,ICP,FT-IR,and UV-Vis and subjected to H2O2-mediated styrene epoxidation.The effects of ratio of organic species to inorganic species and the mole ratio of melamine to thiourea on catalytic performance of the ultimate catalysts were investigated firstly.Successively,effects of reaction time,reaction temperature,amount of oxidant,Au loading and amount of catalyst on the styrene epoxidation were investigated systematically.It was found that,under optimization conditions,the styrene conversion and the selectivity to styrene oxide observed for the catalyst fabricated by the hydrothermal process were 94%and 93%,respectively,whereas the catalyst fabricated by the microwave-heating process showed 99%styrene conversion with 98%selectivity to styrene oxide.Moreover,the both catalysts can be reused for 5 times without significant loss of activity.