Synthesis Of Diphenyl Carbonate By Oxidative Carbonylation Of Phenol Over Pd-M(O) Bimetallic Catalysts

Oxidative carbonylation of phenol is a green route for the synthesis of diphenyl carbonate?DPC?from phenol,CO and O₂ in the presence catalysts.Since the 1980s,the method has been investigated widely by the scholars at home and abroad.Compared with the other two methods?phosgene method and transesterification method?,the oxidative carbonylation of phenol shows the low activity and high price for the catalyst,which can not meet the requirements of industrial production.Therefore,the key to this process lies in the selection of catalysts with high activity,stability and selectivity,especially heterogeneous supported-palladium catalysts.During the preparation and application of the supported-palladium catalysts,there are problems such as agglomerates of active centers,easy deactivation?production of Pd⁰?,poor stability,and so on.The redox agents and preparation methods have a great influence on the activity of the catalyst.In the thesis,the effects of the addition of Cu and Ni as the second metal component and the prepared methods on active components and carriers have been studied in detail,and the reason for the properties of catalysts were discussed by different characterization techniques such as XRD,H₂-TPR,TEM,XPS,and EDS.The technology conditions for the oxidative carbonylation of phenol to DPC were optimized.1.Pd-Cu?Ni?bimetallic catalysts were prepared by deposition–precipitation method with hollandite-type Pb_2-xMn₈O₁₆ used as the carrier,and their activities were evaluated in the oxidative carbonylation of phenol.The active components in the low-load bimetallic catalyst were highly dispersed,which made it be easier for the regeneration of Pd²⁺from Pd⁰ formed in the reaction;the strong interaction between the second metal component?Cu or Ni?and Pb_2-xMn₈O₁₆ has changed the distribution of Mn elements on the surface and enhanced the oxygen storage capacity of the catalyst;the strong interaction between Pd and Cu or Ni changed the electron structure of Pd.All of above factors can promote the cycling of Pd²⁺?Pd⁰,which results in the improvement of the yield of DPC.Among the catalysts,Pd1Cu1,Pd1Cu2,Pd1Cu4 and Pd1Ni4 catalysts exhibit the DPC yield of 22.2%,23.4%,21.5%and 22.8%respectively.Compared with the DPC yield of9.8%over the monometallic catalyst,the yield over the bimetallic catalysts increased about 12%.2.When Pd1Cu4 prepared by the deposition–precipitation method was used as the catalyst in the oxidative carbonylation of phenol,the yield of DPC can reach to 40.6%under the optimum conditions of reaction temperature of 65°C,total pressure of 5.0 MPa,7%content of O₂,stirring speed of 600 r/min and reaction time of 16 h.3.Palladium catalysts supported on hollandite-type Pb_2-xMn₈O₁₆ oxides were prepared by reduction process with ethylene glycol?EG?,HCHO and NaBH₄ used as reductants in H₂O.The structure of Pb_2-xMn₈O₁₆ is destroyed when NaBH₄ is used.The distribution of nano-palladium particles with EG as the reducing agent is more uniform than that with HCHO as the reductant,and the average size of Pd particles is 4.1 nm.The addition of reductants lowers the valence state of Mn element on the surface of catalysts,and increases the number of oxygen vacancies,which are beneficial for the transformation of different oxygen species and enhance the rate of Pd⁰oxidized to active Pd²⁺.The highest yield of diphenyl carbonate was 37.5%when Pd/Pb_2-xMn₈O₁₆prepared by EG catalyzed phenol reaction for 24h.4.A series of supported Pd catalysts with Pb_2-xMn₈O₁₆ as the carrier were prepared by photoreduction method and strong electrostatic adsorption.Compared with the large-size Pd catalysts prepared by the precipitation method,the active Pd with quasi-atomic-level particles in the catalysts by the photoreduction method and strong electrostatic adsorption method were uniformly dispersed on the support.The DPC yields on Pd-Ph and Pd-SEAopt were 19.5%and16.6%respectively after 4h,higher than that on Pd/Pb_2-xMn₈O₁₆ prepared by liquid-phase precipitation reduction under the same reaction conditions.