Preparation Of Magnesium Fluoride And Chromia Catalysts And The Activity For Dehydrofluorination

C-F bonds are extremely polar and stable in fluoroolefins.Fluoroolefins uaually have high corrosion resistance and are widely used in various areas.They are not only very important chemical intermediates,but also raw materials for producing fluorine-containing fine chemical products and polymer materials.In addition,some fluorine-containing alkenes have very low GWP and ODP values,and hence they are good substitutes for refrigerants.At present,gas phase catalytic process is the most promising method for dehydrofluorination of fluoroolefins,but also has high selectivity and low energy consumption.The catalytic performance of different catalysts prepared by different methods was investigated.The physical parameters,acidity and morphology grain size of the catalyst were studied by BET,XRD,NH₃-TPD,SEM,TEM,EDS and other characterization methods.The performance of dehydrofluorination has been focused on.MgF₂ catalyst was prepared by electrospinning.MgF₂ catalyst with fiber structure was prepared by electrospinning combined calcination with Mg?Ac?₂·4H₂O?PVP?PVDF and DMF as raw materials.The catalyst shows high activity and good stability in that dehydrofluorination of R143a.The reaction rate is about 5-7 times higher than that of MgF₂ prepared by conventional precipitation method.The results show that the fiber structure MgF₂ prepared by electrospinning can effectively inhibit the increase of grain size caused by the sintering of catalyst at high reaction temperatures,and has strong acid strength center,which can be attributed to the higher reaction rate.Electrospinning combined with high-temperature carbonization successfully prepared MgF₂/C catalysts with mosaic fiber structure by using Mg?Ac?₂·4H₂O,PVP,PVDF,and DMF as raw materials.Catalysts exhibits high activity in catalytic dehydrogenation reaction of R143a.The reaction rates at 450?and 500?are about2.5 times higher than pure MgF₂ prepared by conventional precipitation method.It was found that MgF₂ embedded in the C fiber is uniformly distributed,and the grain size is extremely small.The embedded MgF₂ hardly shows a larger size during the high-temperature catalytic reaction,which attribute to the higher activity.Cr₂O₃ catalyst was prepared by solution combustion method with Cr?NO₃?₃·9H₂O and glycine?fuel?as raw materials.The catalytic properties of dehydrofluorination of HFC-245fa were studied.The results show that Cr₂O₃ catalyst prepared by solution combustion method has obvious advantages over precipitation method and commercial catalyst.At 300?,the activity of Cr₂O₃ catalyst is 1.5 and 30times higher than that of precipitation method and commercial catalyst,respectively.