Study On The Supported TiO₂ Catalysts For The Transesterification Of Dimethyl Oxalate With Phenol

Much attention has been paid to the synthesis and application of Diphenylcarbonate (DPC) because it can be used as an environmentally benign chemicalintermediate. The transesterification of dimethyl oxalate (DMO) with phenol todiphenyl oxalate (DPO) followed by decarbonylation of DPO to DPC is a promisingnon-phosgene route. In this thesis, the transesterification of dimethyl oxalate (DMO)with phenol over heterogeneous catalysts were studied, and supported titania catalystswere investigated in detail focused on the preparation conditions and activityperformance.By means of BET, XRD, Raman, ICP, XPS, NH3-TPD, and FT-IR analysis ofadsorbed pyridine, it can be concluded that the catalytic activities of supported titaniacatalysts were mainly due to the high dispersion of TiO₂ on the support and the weakLewis acid sites on the catalyst surface.The catalytic properties of TiO₂/SiO2 were closely related with the state oftitania, and the TiO₂ species in the form of amorphism was responsible for thesynthesis of MPO and DPO. Increasing the loading amount of titania and calcinationtemperature led to the formation of TiO₂ crystalline, accordingly, the active propertiesof TiO₂/SiO2 catalyst decreased.Characterization and consideration of the incorporation model indicated that thedispersion capacity of TiO₂ on silica is about 4.1 TiO₂ / nm2 SiO2, corresponding, theactual loadings of TiO₂ 11.1wt.%. The TiO₂/SiO2 catalyst with TiO₂ loading arounddispersion capacity performed best, giving 66.7% conversion of DMO and 99.5%total selectivity to MPO and DPO.The acid strength of catalysts, which greatly affected by the physical-chemicalproperties of support, the loading amount of titania and calcination temperature, had asignificant influence on the selectivity of products. The uniquely existed weak Lewisacid sites in the TiO₂/SiO2 catalyst resulted in high selectivity to MPO and DPO.TiO₂-SiO2 mixed oxides were prepared by sol-gel method. XPS and TEMinvestigation showed that most TiO₂ species inserted into the silica framework,suggesting the strong association of TiO₂ and silica via the formation of the Ti-O-Sibond and homogeneous dispersion of TiO₂ in TiO₂-SiO2 catalyst system. Accordingly,TiO₂-SiO2 catalysts showed high selectivity to target products, DPO. Especially, thepresence of Sn in TiO₂-SnO2-SiO2 catalyst promotered the selectivity to DPO.