Study On Direct Synthesis Of Diphenyl Carbonate With Heterogeneous Catalytic Reaction

The direct synthesis of diphenyl carbonate(DPC) by oxidative carbonylation of phenol with CO and O2 is a promising synthetic method because of its simple process, cheap raw material and environmental benign"green method". The Cu-Co-Mn mixed oxides were prepared by sol-gel method, which were used as the support of the catalyst for the direct synthesis of DPC by heterogeneous catalytic reaction. A new supported catalyst PdCl2-Co(OAc)2/Cu-Co-Mn mixed oxides with high activity was investigated, the catalytic activity of which was evaluated. The optimum conditions for synthesis of the support were determined by orthogonal experiments, and effect of cerium doping on the catalytic activity and byproduct of the reaction was examined. At last, the effects of reaction conditions and reusability of the catalyst were studied.The palladium complexes catalyst system (PdCl2-Co(OAc)2/Cu-Co-Mn mixed oxides--TBAB-H2BQ) has been developed by chosen of the active component and the support. TBTA is known to act both as stabilizing agent for Pd2+, and as surfactant agent for Pd0 complexes. H2BQ promotes the reoxidation of Pd0.The optimum conditions for synthesis of Cu-Co-Mn mixed oxides by sol-gel method were determined by orthogonal experiments. The results indicate that under the optimum reaction conditions of molar proportion of Cu, Mn, and Co being 1:1:1, temperature of calcination 700 oC, drying at 100 oC, and temperature of water bath 85 oC, the yield and selectivity of DPC in the process can reach 38 % and 99 % in the batch operation, respectively. The molar proportion of Cu, Mn, and Co is the first important factor influencing the yield and selectivity of DPC, and temperature of calcination is the second one.The catalyst was characterized by X-ray power diffraction(XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy(EDS), and X-ray photoelectron spectroscopy(XPS). The results show that the size of the particles is in the range of 40~50 nm. The main crystal phase in catalyst is Co2MnO4, and the exist of stable crystal phase Co2MnO4 may contribute to reduce the leaching of active component. The oxygen atoms in the crystal lattice lose electrons and form oxygen vacancies.The increase of oxygen vacancies destroys the crystal integrity and prompts the oxygen adsorption on the crystal surface. This accelerates the oxygen gas transition to crystal oxygen and promotes the regeneration of catalyst, therefore, the catalytic activity is also improved.Effect of cerium doping on the catalytic activity and byproduct of the reaction in the oxidative carbonylation of phenol to DPC over the catalyst PdCl2-Co(OAc)2/Cu-Co-Mn mixed oxides was studied. For catalytic activity, catalyst without Ce shows higher activity than catalyst with Ce under the same conditions, and the yields of DPC for the two catalysts can reach 30% and 23%, respectively. However, for the byproduct of the reaction, cerium doping can prevent the formation of 2-hydroxyphenyl benzoate and p-bromophenyl phenyl carbonate.Effects of reaction temperature, time, pressure and the reusability of the catalyst on the activity were examined. The suitable reaction conditions are determined, and the highest yield of DPC is 40 %. With the increase of reusability time of the catalyst, the activity reduces. The catalyst deactivity is due to both the change of the valency of Pd and Cu , and the decrease of specific surface areas.