Study On The MoO₃/TiO₂-SiO₂ Catalysts For The Transesterification Of Dimethyl Oxalate With Phenol

Diphenyl carbonate (DPC) is a starting material for non-phosgene production of polycarbonates (PCs), which are excellent engineering thermoplastics and substitutes for metals and glasses. Much attention has been paid to the DPC synthesis. And the transesterification of dimethyl oxalate (DMO) with phenol to diphenyl oxalate (DPO) followed by decarbonylation of DPO to DPC is a promising route. In the paper, the process of methyl phenyl oxalate (MPO) and DPO synthesis from the transesterification of DMO with phenol has been studied, and MoO₃/TiO₂-SiO₂ catalysts were explored in detail focused on the acitivity and the surface properties.The shapes of the support and the impregnation methods for the catalysts have some effect on the activity and selectivity of the catalysts. Thereinto, MoO₃ supported on SiO₂ (4 mm particle, surface area 146 m²/g) catalysts showed excellent catalytic efficiency. As a kind of simple, clean and new impregnation method, Slurry impregnation method belongs to the equilibrium adsorption methods and the maximum amount of deposited MoO₃ corresponds to a saturated monolayer.MoO₃/TiO₂-SiO₂ is a kind of novel catalyst wich is very stable, active and selective for the transesterification of DMO with phenol. Compared to MoO₃/SiO₂ catalyst, MoO₃/TiO₂-SiO₂ provides higher DMO conversion in general and more selective to DPO in particular.The results of XRD, BET, XPS, ICP and FT-IR suggested that the dispersed TiO₂ on SiO₂ could enhance the interaction between MoO₃ and SiO₂, and improve the dispersion capability of MoO₃ on the surface of SiO₂, then further improve the catalytic activity. The results of NH₃-TPD and FT-IR of absorped pydine showed that the addition of TiO₂ supplied more weak acid sites including both Lewis and Br?nsted acid sites on the surface of MoO₃/TiO₂-SiO₂, and formed a kind of tetrahedral MoO₃ surface species which was more active.The results indicated that the improvement of catalytic efficiency of MoO₃/TiO₂-SiO₂, compared to MoO₃/SiO₂, could be ascribed to the increased dispersion capacity of MoO₃, the improved surface area of catalysts, the dominant weak acid sites, and the"coordinatively unsaturated"surface MoO₃ species.