The Preparation Of Spherical Catalyst And Its Performance Study In Phenol Oxidative Carbonylation Reaction

Diphenyl Carbonate?DPC?is an important intermediate in the preparation process of thermoplastic Polycarbonate?PC?.The main industry synthesis method of DPC is phosgene method.Due to the reaction using toxic phosgene and it not meet the requirement of low carbon economy development mode,it needs to develop a new green synthetic process to replace.Oxidative carbonylation method is simple and environmentally,which had become the main direction of research and development at home and abroad.The homogeneous catalysis was found to corrosion of equipment and difficult of separation.The present study focused on developing high activity and selectivity heterogeneous catalyst.But the developed catalysts,such as Pd/La_0.5Pb_0.5MnO₃?Pd/OMS-2,are powder catalyst and difficult to separation and recovery.This paper intends to use the oil-ammonia drop method for preparation of spherical lead manganese composite oxide support.The support was loaded by Pd and then use to catalytic oxidation of phenol carbonyl synthesis of diphenyl carbonate.Moreover the used catalyst was recovered to investigate deactivation reasons of supported palladium catalysts for the oxidative carbonylation of phenol.In the Catalyst forming experiments,A series of spherical Pb-Mn composite oxide supports have been prepared via oil-ammonia column method.The crystal structure,surface area,pore volume and pore size distribution of spherical supports were characterized by XRD and BET techniques.The results showed that the specific surface area of the supports increased first and then decreased with the increase of calcination temperature.The maximum specific surface area was 100.09 m2·g-1 at the calcination temperature of 450?.The corresponding XRD patterns showed carbonate precursor was decomposed into MnO₂ and Pb₃O₄ at thiscalcination temperature.The crushing strength of spherical Pb-Mn composite oxide supports decrease with the increasing calcinations temperature.While the calcination temperature exceeded 530 ?,the crushing strength of the spherical supports was significantly elevated.0.5wt% Pd was loaded on spherical supports and used in the oxidative carbonylation of phenol,the best DPC yield reached 11.20% and the selectivity up to 99.1%.In Catalyst deactivation experiment,Palladium catalysts supported on manganese oxides octahedral molecular sieves?OMS-2?,Pb doped OMS-2?Pb-OMS-2?and perovskite-type La_0.5Pb_0.5MnO₃ were prepared and the deactivation causes of catalyst were investigated during the oxidative carbonylation of phenol.The experimental results of catalytic test on three different sets of catalyst demonstrated that all were inactive after continuous reaction for 22 h.XRD patterns and HRTEM images demonstrated that carbonaceous pollution and palladium leaching occurred during the reaction progress.ICP-AES analysis revealed that the solvent and oxygen atmosphere had a significant impact on the palladium leaching.In addition,hot filtration tests and SH-HZSM-5 adsorption studies indicated that the leached palladium species were not active species.The results of XPS patterns and H₂-TPR profiles showed that Pd???was the active species and surface oxygen species could re-oxidize Pd?0?to Pd?II?.In summary,consumption of oxygen species,Pd leaching and carbonaceous pollution hindered the re-oxidation recycling of palladium,which resulted in the deactivation of supported palladium catalysts for the oxidative carbonylation of phenol.