氟化镁基催化剂催化2-氯-1,1,1,2-四氟丙烷气相脱卤化氢反应性能研究

Gas-phase dehydrohalogenation of 2-chloro-1,1,1,2-tetrafluoropropene over magnesium fluoride-based catalysts

采用等体积浸渍法制备了不同金属离子(M^(n+))改性的系列氟化镁基催化剂(M/MgF_2),考察了其在高温气相条件下催化转化2-氯-1,1,1,2-四氟丙烷(HCFC-244bb)合成新一代环保制冷剂2,3,3,3-四氟丙烯(HFO-1234yf)的反应性能。实验结果表明,单一氟化镁上同时存在脱HF、脱HCl 2种反应过程,但前者为主反应,脱HF生成副产物2-氯-3,3,3-三氟丙烯(HCFO-1233xf)的选择性达87.7%,目标脱HCl产物HFO-1234yf选择性不足10%。Al^(3+)改性后,催化剂活性显著增加,但脱HF选择性也随之增大(约90%)。3%Fe/MgF_2、3%Zr/MgF_2催化剂上HFO-1234yf选择性有所提高,但不足20%。碱金属K^+、Cs^+的添加可大幅提高催化剂的脱HCl选择性,分别为76.4%和86.6%,但催化剂活性低于未改性MgF_2催化剂。采用N_2物理吸附、NH_3-TPD等表征手段对催化剂结构、表面酸性进行表征,并将其与催化反应性能进行关联,结果表明,催化剂表面酸性的减弱有利于反应向选择性脱HCl方向移动。

A series of magnesium fluoride-based catalysts（ M/MgF_2） modified by different metal ions（ M^（n＋）） are prepared by equal volume impregnation method and their catalytic performances are investigated in the gas-phase catalytic dehydrochlorination of 1,1,1,2-tetrafluoro-2-chloropropane（ HCFC-244 bb） to make 2,3,3,3-tetrafluoropropylene（ HFO-1234 yf）,a new generation of environment-friendly refrigerant. It is found that both dehydrofluorination and dehydrochlorination reactions occur on the pure MgF_2 catalyst,with dehydrofluorination as the main reaction.More importantly,the dehydrochlorination selectivity to HFO-1234 yf is only 8. 8%,and the selectivity to 2-chloro-3,3,3-trifluropropylene（ HCFO-1233 xf） is as high as 87. 7%. The catalyst modified by Al^（3＋）exhibits higher activity,however,the un-expected dehydrofluorination selectivity to HCFO-1233 xf increases to around 90% over the catalyst modified by Al^（3＋）,although.The dehydrochlorination selectivity to HFO-1234 yf over 3%Fe/MgF_2 or 3% Zr/MgF_2 catalysts increases,but still less than 20%.High dehydrochlorination selectivity can be achieved over the MgF_2 catalysts modified by K or Cs halides,reaching 76. 4% and 86. 6% respectively,however,the activities of these catalysts are lower than the pure MgF_2 catalyst.The structure and surface acidity of prepared catalysts are characterized by means of XRD,NH_3-TPD and N_2 physical adsorption measurements,which are then correlated with catalytic performance. The results show that decreasing the surface acidity of catalyst can benefit the dehydrochlorination of HCFC-244 bb.