Study On The Supported MoO₃ Catalysts For The Synthesis Of Diphenyl Oxalate From 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 because of their good impact strength and transparency. Several alternative non-phosgene methods for DPC synthesis have been proposed. Among them, the transesterification of dimethyl oxalate (DMO) with phenol to diphenyl oxalate (DPO) followed by decarbonylation of DPO to DPC is a promising route. It is an environmentally benign process with the mild reaction condition, no azeotrope mixture formed and easy separation of co-products methanol and CO from reaction system. In the thesis, the process of methyl phenyl oxalate (MPO) and DPO synthesis from the transesterification of DMO with phenol has been studied.Various oxides and supported oxides were investigated and the evaluation results showed that MoO3/SiO2 catalysts had a better activity and excellent selectivity to target products. The Mo loading had an obvious effect on the catalytic performance of ester exchange reaction. The MoO3/SiO2 catalyst with 1 wt% Mo content performed best, giving 54.6 % conversion of DMO and 99.6% selectivity to MPO and DPO.The catalytic properties of MoO3/SiO2 were closely related with the state of molybdenum. MoO3 was highly dispersed on the surface of silica as amorphous state at low Mo loading, while crystallized into bulk MoO3 at high Mo loading. The Mo species in the form of amorphism is more responsible than that of crystalline MoO3 for the synthesis of MPO and DPO.The dispersion of MoO3 active centers on the surface of high area support enhanced catalytic activities. The acid strength of support MoO3 catalysts had a significant influence on the selectivity of products. The peaks above 450K can be attributed to the desorption of NH3 from moderate or strong Br?nsted and Lewis type acid sites, and the assignment of the peaks below 450K is contributed to the desorption of NH3 from weak acid sites. The weak acid sites were in favor of the formation of MPO and DPO through the cracking of acyloxy bond, while the moderate and strong acid sites took advantage of generation of byproduct, anisole, through the cracking of alkoxide bond.By means of BET, XRD, XPS, NH3-TPD, and FT-IR analysis of adsorbed pyridine, it can be concluded that the catalytic activities of MoO3-SnO2/SiO2 were correlated with the state of Mo and Sn, and the acid type, acid strength, and acid amount on catalyst surface. The presence of Sn promoter decreased MoO3 crystalloid on SiO2 surface and led to a better dispersion of the molybdenum phase. The integrated effect of the synergy of Sn with Mo-O-Si and weak Lewis acid sites catalyzed transesterification of DMO with phenol.Slurry impregnation method exhibited higher activity and dispersion capacity compared to the MoO3/SiO2 prepared conventionally. Slurry MoO3/water is used instead of the solution ammonium heptamolybdate. Highly dispersed amorphous Mo catalysts are obtained, which is closely related the catalytic activities, without calcination, waste solutions, and calcining nitrogenous gases. The dependence of catalytic activity on Mo loading for the slurry prepared catalysts was similar to the samples prepared by the conventional impregnation method, indicating the slurry method is a simple and clean alternative to the conventional one.