SiO2改性MCM-22分子筛上联苯与环己醇的择形烷基化反应

摘要

以正硅酸四乙酯(TEOS)为修饰剂,采用化学液相沉积法(CLD)对MCM-22分子筛进行改性,制备了一系列SiO2改性的MCM-22催化剂.采用X射线衍射(XRD)、N2物理吸附-脱附、氨程序升温脱附(NH3-TPD)、吡啶吸附红外光谱(Py-IR)对催化剂性质进行了表征.结果表明SiO2主要沉积在MCM-22分子筛的外表面,外表面上的Brφnsted酸位量明显减少,但对分子筛的总酸量影响不大.考察了改性催化剂用于联苯与环己醇的择形烷基化反应制备线性4-环己基联苯(4-CBP)及4,4’-环己基联苯(4,4'-DCBP)的催化性能.在常压条件下,温度为190℃时反应200 min,4-CBP与4,4’-DCBP的选择性分别为80.4％与63.7％.结合表征数据,发现SiO2沉积对发生在催化剂外表面Brφnsted酸位上的异构化反应有明显的抑制作用.此外,重复使用5次后的改性分子筛经过焙烧复原,活性与选择性基本恢复.%Shape-selective catalysts for alkylation of biphenyl with cyclohexanol were prepared by modification of MCM-22 zeolite using chemical liquid deposition (CLD) process with tetraethyl orthosilicate (TEOS).The modified MCM-22 catalysts were characterized by X-ray diffraction (XRD),N2 physical adsorption-desorption,NH3 temperature-programmed desorption (NH3-TPD),and adsorbed pyridine infrared spectroscopy (Py-IR).The results showed that SiO2 was mainly deposited on the external zeolite surfaces,with no significant structural changes observed in the MCM-22 zeolite after modification.The deposited SiO2 could reduce the number of external Brφnsted acid sites of the zeolites,without noticeably reducing the total amount of acid sites.Shape-selective alkylation of biphenyl with cyclohexanol was carried out over the synthesized catalysts.The selectivity of 4-cyclohexylbiphenyl (4-CBP) and 4,4'-cyclohexylbiphenyl (4,4'-DCBP) reached a maximum of 80.4％ and 63.7％,respectively,when the reaction was carried out for 200 min at 190 ℃ under atmospheric pressure.The characterization data indicated that the isomerization reactions at the external Brφnsted acid sites were diminished effectively.In addition,the catalytic activity of the used zeolites was almost recovered by calcination.