Load Au Ethylene Glycol Catalyzed Oxidative Esterification Of Size Effect And The Effect Of The Carrier

Mmethyl glycolate as a crucial chemical resource has attracted much attention in recent years. The traditional synthesis rouses for methyl glycolate have some shortcomings:expensive raw material cost, severe corrosion in equipment, and difficulty in separation of the products, so it is very necessary to develop an environmentally friendly synthesis method of methyl glycolate. It has been reported that methyl glycolate can be synthesized by oxidative esterization of ethylene glycol over supported Au catalysts. As is known to all, the size of the Au nanoparticles and the nature of the support are essential in determing the catalytic activity, but the roles of the Au size and support types on the oxidative esterification of ethylene glycol are not still clear. Undoubtedly, understanding of the roles of Au size and support on the reaction will be helpful for the rational design of highly-efficiency Au catalysts.In this thesis, nano Au sols with narrow size distribution and high dispersion were deposited on different metal oxides supports by colloidal deposition method and their catalytic activity in the oxidative esterification of ethylene glycol were investigated. Detailed research results are listed as follows:(1) The kind and the amount of protective agents as well as the influence of calcination temperature on the Au particle sizes on Au/ZnO catalysts were investigated; the optimum prepared conditions for supported Au catalyst are as follows:calcination temperature is300℃, protective agent is PVA, and the amount of PVA is Au/PVA=2:1mg mg-1.(2) Au/ZnO catalyst with four different Au mean particle sizes (2,3,5and8nm) have been successfully prepared by adjusting the temperature of synthesis Au sols, meanwhile the role of Au size in the reaction is also examined. The results suggest that the catalytic activity is poorer when the Au particle size is below2nm or above5nm, the best catalytic performance can be obtained only when the Au particles diameter is near3nm.(3) A series of Au catalysts with lwt%Au loading and uniform mean nanoparticle size (-3nm) supported on five different metal oxide-supports (ZnO, Al2O3, SiO2, TiO2, CeO2) has been prepared. The possible influencing factors of support acidity, the chemical state of Au species, and the Au content onto Au catalytic activity were studied by XRD, HRTEM, BET, H2-TPR, NH3-TPD, and XPS. The results suggest that: metallic gold is the main active species in catalytic oxidative esterification of ethylene glycol. The catalytic activity of Au catalysts is closely related with the stability effect of support to Au particles, acidity of supports, and activation of O2on the interface of Au-support.