Characterization Of Supported Wacker-Type Catalysts In Vapor-Phase Dimethyl Carbonate Synthesis

As a green chemical intermediate, dimethyl carbonate (DMC) is a safe substitute for dimethyl sulphate and phosgene in many industrial processes due to the carbonyl and the methyl group. With development of many new processes, much more DMC is needed as an intermediate in the synthesize polycarbonates and isocyanates etc., especially for using as a very good blending component and an outstanding oxygenating agent for environmental gasoline. Great effects have been dedicated to study and development of new environmental friendly processes for the synthesis of DMC.Compare to the traditional phosgene process, synthesis of DMC by oxidative carbonylation of methanol is more favorable because of its simple, environmental benign and cost-effective characters. This process could be operated in liquid or gas phase, and the gas phase process is more desirable by offering advantages to overcome the shortcomings, such as severe corrosive, separating difficulty and a short service life, associated with the liquid process. One of the gas phase routes is the methyl nitrite process, in which methanol is first converted into methyl nitrite (CH3-ONO) and then into DMC via reaction with CO. The use of this route results in complex process and additional toxicity concerns due to the use of nitric oxide. Therefore, the synthesis of DMC by the new vapor phase oxidative carbonylation of methanol is more reasonable, cost-effective and matching the development of green chemistry.In this dissertation, the Wacker-Type, PdCl2-CuCl2 bimetallic catalyst system has been systematically investigated for DMC synthesis by oxidative carbonylation of methanol in atmospheric pressure. The influences of different factors on the catalytic performance were studied in detail. Multiple techniques including BET, XRD, TPR, SEM/EDX, in situ DRIFTS, EPR etc were used to characterize the morphological and electronic structure of the catalysts and mechanism of the reaction.1. Activated Carbon Supported Wacker-Type CatalystsCatalysts with different active component, different promoter, different quantities of KOAc were made by conventional impregnating method. It was found that the catalyst with only one metallic chloride had little catalytic activity at atmospheric pressure. There was the optimal ratio between the two active components, suggesting the presence of a synergetic effect for the active components of palladium and copper on the catalytic performance in the present bimetallic catalyst system. Among the promoters used in our catalysts, KOAc was the best one. The proper mole ratio of KOAc/CuCb was 1.0. Based on all of the experimental observations and structural, morphological analysis (XRD, SEM), it could be conclusively said that appropriate amount of KOAc addition helps enhancing the performance of catalysts by forming intermediate species, Cu2Cl(OH)3, in DMC synthesis reaction. In a higher KOAc/CuCl2 mole ratio region, many KC1 appeared and was interpreted to block the active sites of catalysts.In order to evaluate the effect of surface characters of activated carbon on catalytic performance, the activated carbon (GH-1) subjected to different chemical treatments was investigated. BET result showed that the pretreatments did not change surface area and structure of supports drastically. However, based on FTIR, TPD, XPS and titration results for these pretreated supports, we found that surface property of activated carbon was modified by these treatments. Up on the HNO3 or Air treatment, acidic, hydrophilic groups increased on the surface of activated carbon. Water, KOH and H2 reduction treatment kept or increased basic hydrophobic groups on the surface of supports. The XRD results for catalysts indicated that acidic groups was disadvantageous of forming of Cu2Cl(OH)3. EPR , XPS , SEM and TPR characterization proved, active components were dispersed highly on the surface of support due to these acidic groups. Well-dispersed active components in the micro pore of support were explained to show poor catalytic performance and selectivity d...