| Diphenyl carbonate?DPC? is an important organic carbonic ester which is mainly used as a chemical raw material intermediate or to produce polycarbonate?PC? in plastic industry.Phosgene method is the main method for industrial production of DPC among other methods as transesterification and oxidative carbonylation.Due to toxicity of reactant phosgene and corrosiveness of resultant chlorine hydride,the one-step green process of synthesizing DPC by oxidative carbonylation has great development value and application prospect.The heterogeneous bimetallic oxide Pd-support catalysts were usually used in synthesis of DPC by oxidative carbonylation of phenol reaction for the advantages of easy recovery of the catalysts and environmentally friendly process,and the catalysts were easily separated and recovered from the resultants.However,some problems,such as carbon deposition of active constituents and cementation of active centers,were existed in these catalysts.The improvements of catalytic performance in heterogeneous systems were closely related to the promotion of selected redox promoters.Therefore,it was significant to optimize the selection of promoters and carriers.For instance,because of the synergistic effect between metal oxides,the redox ability of the bimetallic oxides was better than that of the single metal carriers,and the bimetallic oxides were adopted to enhance the catalyst activity.In this paper,Mn doping W,V and Bi bimetallic composite oxides carriers were prepared by coprecipitation method,in which Pd Cl2 was used as active component to prepare supported catalysts and was studied in one-step synthesis of diphenyl carbonate by heterogeneous catalytic oxidation carbonylation of phenol.The effects of different doping metals on the activity of catalysts,different doping ratios and calcination temperatures on the structure of catalyst carriers and oxidation state on the catalytic performance of catalysts were investigated experimentally.The structure and surface properties of the catalyst were characterized by gas chromatography?GC?,X-ray diffraction?XRD?,hydrogen temperature programmed reduction?H2-TPR?,X-ray photoelectron spectroscopy?XPS?.The main contents and results of this study are as follows:?1?Due to the increasing doping ratios and calcination temperatures of Mn-W bimetallic composite oxide,partial manganese ions doped in the carrier were increased from Mn2+ to Mn3+,and W was permeated into the crystal lattice of MnOx and then the metal oxide carriers containing MnWO4 and Mn3O4 were formed.When prepared at a doping ratio of 1:1 and a calcination temperature of 600°C,the best catalytic activity could be obtained,the yield and selectivity of DPC were 5.2% and 98.5%respectively.?2?MnO2 crystalline phase was formed when the Mn-V doping ratio was 1:5 and its catalytic activity was obviously improved,the yield and selectivity of DPC were 10.46%and 99.4% respectively.However,the crystallinity of Mn-V bimetallic oxide carrier was greatly influenced by temperature.Its crystalline form could be destroyed by higher calcination temperature which counted against the isolation and integrity of Mn-V oxide crystalline form,resulting in a significant decrease of its activity.?3?Lower calcination temperatures were conducive to the formation of Mn-Bi bimetallic composite oxides and the formation of MnO2 at 400? made the oxidation performance of the carriers more prominent.When Bi doping ratio was increased,in virtue of the destruction of the crystal form of the carriers,the catalytic performance began to decline.While,when the doping ratio was 1:5,the best oxidation performance and the highest catalytic activity could be achieved,the yield and selectivity of DPC were 13.13%and 99.6%respectively.?4?By comparing the structure and catalytic performance of bimetallic catalysts with single metal catalysts,bismuth-manganese bimetallic catalysts had the best catalytic performance.Meanwhile,the catalytic mechanism of Mn-Bi bimetallic composite oxides was preliminarily discussed. |
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