Study On The Supported Wacker Type Catalysts In The Oxidative Carbonylation Of Ethanol To Diethyl Carbonate

Oxidative carbonylation of ethanol for preparation of diethyl carbonate (DEC) offers prospects for a"green chemistry"replacement of phosgene for polymer production and other processes. Over past years, diethyl carbonate has been found to be a substitute for methyl tert-butyl ether (MTBE), which is used as an oxygen-containing fuel additive. Wacker type catalysts for the (gas-phase) oxidative carbonylation of ethanol to diethyl carbonate have been discussed and present in this dissertation.We report on the effect of promoters on catalytic activities in the oxidative carbonylation of ethanol to diethyl carbonate and the results have shown that KCl is the best promoter. Additionally, KCl favors crystalline Cu(OH)Cl formation, which plays a decisive role in the DEC synthesis. An electron transfer effect of Pd-Cu in the Wacker type catalyst has been proved by ESR analysis of copper species and XPS analysis of palladium species. We have also presented evidence that deactivation of catalysts can be ascribed to the leaching of Cl species that is a possible intermediate in electron transfer between Pd and Cu, which leads to the formation of a large amount of Pd0. DRIFT analysis of surface functional groups on the Wacker type catalyst indicates that the presence of main product and by products result in an increase in polar groups on the surfaces of the catalysts, which causes a decrease in the catalytic activities.In-situ XRD studies on the CuCl2-PdCl2-KCl-NaOH catalyst shows that thermal pretreatment on the catalyst significantly alters the structures catalyst crystal. A optimal thermal pretreated temperature has been obtained at 523 K, which favors the formation of Cu(OH)Cl.Modifications of surface groups on the activated carbon via different type of plasma have been discussed. O2 plasma is found to be favored for the formation of hydroxyl groups, while H2 plasma improves the production of lactone groups. However, surface group of carboxyl is not sensitive to the type of plasmas. In addition, pretreatment of activated carbon provides increased amount of oxygen containing group on the activated carbon surfaces and enhances the dispersion of Cu species on the supports.Quasi in-situ XPS, XRD and in-situ DRIFT investigations on the catalytic system indicate that the reaction involves a multiple steps in the oxidative carbonylation of ethanol to diethyl carbonate, e.g., dissociative adsorption of ethanol; chemisorption of CO, and the insertion of CO. Oxygen is involved in the reaction as a gas phase. Chloride species plays a significant role in the cycle of reaction and besides, Pd-Cu electron transfer process in the catalyst promots the reaction, Basen on these experimental results, a reaction course of oxidative carbonylation of ethanol to diethyl carbonate over Wacker type catalyst has been proposed..