Preparation Of Magnesium And Zirconiumaluminophosphate And Catalytic Performancefor Synthesis Of Methyl Ethyl Carbonate

As the demand for lithium-ion batteries increases,the synthesis of ethyl methyl carbonate（EMC）has attracted much interest since it can be utilized as an excellent cosolvent in the nonaqueous electrolyte.The transesterification of dimethyl carbonate（DMC）and diethyl carbonate（DEC）is considered as a promising approach for the synthesis of EMC due to that all the reaction mixtures（DEC,DMC and EMC）can be used as solvents in non-aqueous electrolytes,which could greatly reduces the cost of separation.The key to the implementment of this route is to develop efficient and stable catalaysts.The amorphous metal aluminophosphate catalysts with acid-basic sites were prepared and used to investigate the catalytic performance for the transesterification of diethyl carbonate and dimethyl carbonate.Firstly,the amorphous magnesium substituted mesoporous aluminophosphate（MgAPO）with acid-basic sites were prepared by the citric acid template decomposition method.The composition,textural and morphology of MgAPO were characterized by XRD,FT-IR,XPS,N₂adsorption-desorption,TGA and SEM,which demonstrated that magnesium successfully substituted aluminum and incorporated into the framework of aluminumphosphate.The catalyst showed high specific surface area and a uniform pore size distribution.The acid and basic properties of the catalysts were determined by CO₂/NH₃-TPD,which indicated the catalyst had different strengh basic and weak acid sites,and the basicity was enhanced with the addition of magnesium.Mg_0.2APO shows remarkable catalytic performance in the transesterification reaction with 55.3%DEC conversion and 95.1%selectivity to EMC in the fixed-bed reactor at 100℃and liquid hourly space velocity（LHSV）of 3.6 h^-1.The excellent catalytic performance of Mg_0.2APO in the transesterification reaction is mainly due to the strong basic and weak acid sites synergistic catalysis.In addition,the activity of Mg_0.2APO remains almost the same even after 500 h of time-on-stream,which indicate the catalyst shows high stability.Second,a series of amorphous bimetallic mesoporous aluminophosphate（MgZrAPO）with different content of magnesium and zirconium were prepared via the citric acid template decomposition method.The composition,textural and morphology of MgZrAPO were characterized by XRD,N₂adsorption-desorption,TGA,SEM and EDX.The results showed that the Mg and Zr highly dispersed in the catalysts with large specific surface area and narrow pore size distribution.CO₂/NH₃-TPD were used to investigate the concentration and strength of basic and acid sites of the catalyst.According to the results of CO₂-TPD and NH₃-TPD,the MgZrAPOs had both different strengh basic and weak acid sites,and the strong basic strength and concentration of the bimetallic MgZrAPO catalysts were significantly enhanced compared to that of monometallic MgAPO.Bimetallic MgZrAPO showed better catalytic activity than monometallic MgAPO,among which Mg_0.1Zr_0.1APO exhibited the best catalytic performance in the fixed-bed reactor at 90℃with the LHSV of6.0 h^-1,in which conversion of DEC and selectivity to EMC were 53.7%and 96.6%,respectively.The result was attributed to the synergistic catalysis of optimum amounts of strong basic and weak acid sites.In addition,there is no obvious differences in the the activity of Mg_0.1Zr_0.1APO even after 500 h of time-on-stream,which indicate the catalyst shows high stability.