Oxidative Carbonylation Of Phenol Catalyzed By Pd/Ce_xZr_1-xO₂

Polycarbonate（PC）is a thermoplastic engineering plastic with excellent performance and wide application.Diphenyl carbonate（DPC）is a raw material for PC synthesis by non-phosgene method.With the rapid development of the PC industry,the demand for DPC has also increased rapidly,so that DPC synthesis research has become a hot spot.The phenol oxidative carbonylation method uses the primary chemical raw materials CO and O₂ to react with phenol in one step to synthesize DPC.It has the advantages of short process flow and cheap raw materials.It is a very promising route for industrial application.Zr-doped Ce O₂ is a widely studied and applied catalyst/support,which not only maintains the oxygen storage capacity of Ce O₂,but also improves its thermal stability;and,the introduction of Zr is beneficial to increase the surface oxygen hole concentration,thereby increasing Its oxidation activity.Ce_0.7Zr_0.3O₂ was prepared by the citric acid sol-gel method,and the supported Pd catalyst(Pd/Ce_0.7Zr_0.3O₂)was prepared by using the incipient wetness impregnation method.Then the catalyst was applied to the oxidative carbonylation of phenol.The effect of carrier calcination temperature on catalytic performance and the role of Zr doping were investigated.The study found that,compared with the Pd/Ce O₂ catalyst,Pd/Ce_0.7Zr_0.3O₂ greatly improved the conversion rate of phenol and DPC selectivity;and the calcination temperature of the carrier also had a significant effect on its catalytic performance.When the carrier calcination temperature is 600℃,Pd/Ce_0.7Zr_0.3O₂ has the best catalytic performance;at this time,the phenol conversion rate is 70.0%and the DPC selectivity reaches 77.2%.Catalyst specific surface area,Ce³⁺or oxygen vacancy content,oxygen species type and Pd（II）content will affect the catalytic performance of Pd/Ce_0.7Zr_0.3O₂ and Pd/Ce O₂,which is the result of their synergistic effect;while Zr doping and The change of the calcination temperature of the carrier acts on the oxidative carbonylation of phenol through the influence on the above properties.Ce_xZr_1-xO₂ with different Ce/Zr ratio（x=1,0.3,0.4,0.5,0.6,0.7）was prepared by citric acid sol-gel method,and the calcination temperature was 600℃;then Pd/Ce_xZr_1-xO₂ catalyst was prepared by incipient wetness impregnation method.It was applied to the phenol oxidative carbonylation reaction,and the effect of Ce/Zr ratio on the catalytic performance of Pd/Ce_xZr_1-xO₂ was investigated.It was found that when Ce/Zr=7:3,the catalytic activity of the catalyst was the best.The phenol conversion rate is 70.0%and the DPC selectivity reaches 77.2%.Characterization found that Pd/Ce_0.7Zr_0.3O₂ has more oxygen vacancies,surface oxygen that is easier to be reduced,and the higher content of Pd（II）active centers on the surface is the reason for its better catalytic performance.