FER分子筛Lewis酸中心对异丁烯催化转化的影响

Effect of Lewis acid sites of FER zeolite on catalytic transformation of isobutene

采用不同浓度六氟硅酸铵(AHFS)对FER型分子筛进行同晶置换改性,制备了一系列具有不同酸类型、酸密度及可接近性等特征的改性FER分子筛样品,运用XRD、N_(2)吸附-脱附等温线等方法对其织构性质进行表征,通过NH_(3)-TPD和Py-FTIR关联改性FER分子筛的酸性质,并结合反应评价系统探究了改性FER分子筛酸中心与丁烯(1-丁烯、异丁烯)骨架异构化反应间的构效关系。结果表明,根据产物收率确定,以1-丁烯和异丁烯分别作为原料时其骨架异构化的最佳反应温度均为350℃,以异丁烯作为原料时副反应更为明显。在脱铝过程中,由于脱铝剂和分子筛中的非骨架铝羟基物种的相互作用,产生了强弱不同的两种新Lewis酸中心,在反应过程中上述两种Lewis酸中心促进了异丁烯齐聚-裂化反应的进行,进而降低了主反应的选择性。

A series of modified FER zeolite samples with different acid types,acid density and accessibility were prepared by using different concentrations of ammonium hexafluorosilicate(AHFS)for isomorphous substitution.The texture properties were characterized by XRD and N_(2) adsorption isotherms.And the acid properties were characterized by NH_(3)-TPD and Py-FTIR.The results showed that when 1-butene and isobutene were respectively used as raw materials,the optimal reaction temperature for skeleton isomerization was 350℃,and the side reaction was more obvious when isobutene was used as raw material.During the dealumination process,two new Lewis acid sites with different strength were generated,due to the interaction between the dealumination agent and the extra framework aluminum hydroxyl species on the zeolite.During the reaction,the above two Lewis acid sites promoted the oligomerization-cracking of isobutene,thereby,reducing the selectivity of the main reaction.