Controllable Fabrication Of Cu-doped Zeolite Catalysts And Support Effect On The Oxidative Carbonylation Of Ethanol

Diethyl carbonate(DEC), as an eco-friendly chemical, is gaining popularitybecause of burgeoning applications in chemical synthesis and lithium batteryelectrolytes, oxygenated fuel additive, etc. The direct synthesis of DEC throughoxidative carbonylation has attracted more attentions concerned within the frame ofgreen chemistry. Although utilization of Cu-doped zeolite catalysts instead of Wackertype catalyst can resolve the deactivation of catalyst and corrosion due to loss ofchlorine, the activity and selectivity of this catalyst system still need improvement forfurther industrial applications. Furthermore, the effect of supports on formation andproperties of active species need further investigation for understanding therelationship between structure and performance. This dissertation focuses onunderstanding of the support effect on Cu active species of Cu-doped zeolite and itscatalytic performance in oxidative carbonylation, aiming to realize controllablefabrication of Cu-zeolite catalyst.In order to eliminate the influences of channel structure, faujasite with variousSiO2/Al2O3ratios and Hβ before and after passivation were investigated for DECsynthesis. Combined with pyridine-adsorption IR and catalytic measurements, aquantitative relationship between amount of Br nsted acidic sites and catalyticactivities for oxidative carbonylation of ethanol has been established. CO-adsorptionIR suggested that the location of Cu active species was influenced by the distributionof Br nsted acidic sites, which also played an important role in catalytic performanceof oxidative carbonylation.NaY was modified with NaOH solutions followed by ion exchange with NH4+toHY. The textural and acidic properties of NaY and its effect on catalytic activity of thecorresponding CuY catalyst were investigated. Alkaline treatment with appropriateconcentration generated defects in the zeolite framework and promoted dealuminationduring ion exchange procedure assisted by microwave radiation, which resulted in thecreation of meso-and macropores in zeolite Y and benefited for the catalyticperformance. In addition, the increased amount of hydroxyl group in supercages andextraframework Al species favored formation of Cu active sites and further yield ofDEC.Y-β composite zeolite was synthetized using preset crystal seeds method. The characterization results demonstrated the Y-β composite zeolite had the structuralfeature of both Y and β instead of a physical mixture. Investigation of preparationconditions indicated that crystallization time, composition and alkalinity in gelaffected the proportion of Y and β in composite zeolite, which had an impact on DECproduction.By introduction of aluminum into mesoporous silica MCM-41, the amount ofBr nsted acidic sites was improved without change in ordered channel structure,which contributed to dispersion of CuCl and further catalytic performance.Preparation methods dominated the activity of CuY in oxidative carbonylation.Compared to other samples, CuY prepared by ammonia evaporation method exhibitedthe optimal catalytic properties. Thermal treatment in inert atmosphere is necessaryfor coordination of Cu+to lattice oxygen of zeolite framework. It is confirmed that thetextural properties, chemical states of active sites and acidity of CuY catalysts wereprofoundly affected by the kinds of copper precursors. Dispersion and valence of Cuspecies related to DEC yield, while moderate acid sites were responsible for DEEproduction. Excess CuOxaggregates resulted in an obvious decrease of Cu+content,surface area and pore volume, which generated a deterioration of DEC selectivity andethanol conversion.