Study On The Solid Oxide Catalysts For The Transesterification Of Diethyl Oxalate With Phenol

Much attention has been paid to the synthesis and application of diphenyl carbonate (DPC) because it can be used as an environmentally benign chemical intermediate. The transesterification of diethyl oxalate (DEO) with phenol to diphenyl oxalate (DPO) followed by decarbonylation of DPO to DPC is a promising non-phosgene route. In this thesis, the transesterification of diethyl oxalate (DEO) with phenol over heterogeneous catalysts are studied. The activity performance of supported TiO₂/SiO₂, MoO₃/SiO₂ and MoO₃/SiO₂ mixed oxides catalysts are investigated in detail.By means of BET, XRD, Raman, ICP, IR, XPS, NH3-TPD and FT-IR analysis of adsorbed pyridine, it can be concluded that the catalytic activities of supported catalysts are mainly attributed to the high dispersion of the catalysts on the support and the weak Lewis acid sites on the catalyst surface.The weak lewis acid sites of TiO₂/SiO₂, MoO₃/SiO₂ and MoO₃-SiO₂ catalysts are the active centers for the transesterification from DEO and Phenol. The merely existed weak Lewis acid sites in the TiO₂/SiO₂, MoO₃/SiO₂ and MoO₃-SiO₂ catalysts result in high selectivity to target products.The catalytic properties of TiO₂/SiO₂, MoO₃/SiO₂ and MoO₃-SiO₂ catalysts are closely related with the state of TiO₂ and MoO₃. The TiO₂ and MoO₃ species in the form of amorphous state is responsible for the synthesis of ethylphenyl oxlate(EPO) and DPO, especially, for the disproportionation of EPO to DPO. When the crystal is formed, the catalyst activity and selectivity to DPO is decreased. Increasing the loading amount of TiO₂ and MoO₃ and improving calcination temperature lead to the formation of TiO₂ and MoO₃ crystalline, accordingly, the active properties of MoO₃/SiO₂ catalyst decreased.The activity of MoO₃-SiO₂ mixed oxides by sol-gel method is better than the supported MoO₃/SiO₂ catalysts. IR investigation shows that most MoO₃ species insert into the silica framework, suggesting the strong interaction of MoO₃ and silica via the formation of Mo-O-Si bond. Accordingly, more acid aites are produced in more dispersed state, resulting in the improvement of the catalytic activity and selectivity to DPO. The catalyst of MoO₃/SiO₂ with 12% MoO₃ performed best, giving 71.0% conversion of DEO, 32.0% selectivity of DPO, 22.7% yield of DPO, and 100% total selectivity to DPO and EPO.