以四甲基铵硅酸盐为柱化剂合成层柱状MCM-36分子筛

以层状MCM-22P为前驱体,四甲基铵硅酸盐为柱化剂,采用动态水热法考察了MCM-36分子筛的合成条件,并通过XRD、N2物理吸附、TEM、27Al-MAS NMR以及NH3-TPD等手段对合成分子筛进行了表征。结果表明,与传统的采用正硅酸乙酯为柱化剂的柱化过程相比,以四甲基铵硅酸盐为柱化剂时,已溶胀的前驱体不经干燥处理即可直接在含水体系进行柱化插层合成得到层间距均一的层柱状MCM-36分子筛,适宜的合成条件为:先在80℃的高pH值(约13.5)环境下对前驱体溶胀24 h,然后在100℃下柱化插层24 h。表征结果表明,MCM-36分子筛具有层内微孔和层间介孔的复合孔道结构以及较大的比表面积(特别是外比表面积);与HMCM-22相比,HMCM-36的表面酸性虽明显降低,但其层间介孔结构的形成使大量B酸中心暴露于大分子易于接近的层间介孔孔壁,可为涉及较大分子的催化反应提供更多可接近的活性位中心。

Synthesis of pillared MCM-36 zeolites with tetramethylammonium silicate as pillaring reagent

Pillared MCM-36 zeolites of MWW type were hydrothermally synthesized by pillaring swollen layered MCM-22P precursor, with tetramethylammonium silicate as the pillaring reagent; the synthesized zeolites were characterized by different physico-chemical techniques such as XRD, N₂ adsorption, TEM, ²⁷Al-MAS, NMR and NH₃-TPD. The results showed that the swollen MCM-22P without drying was successfully pillared in an aqueous solution system; the MCM-36 zeolites with an uniform interlayer distance were then readily obtained. The suitable synthesis conditions for MCM-36 are 80℃ for 24 h for the interlayer swelling of MCM-22P at high pH value (13.5), and then at 100℃ for 24 h for the formation of the intercalating pillars. The MCM-36 zeolites obtained exhibit a typical MWW topology structure, with a composite pore system of both micropores in the crystalline layers and mesopores in the interlayer space, and a large specific surface area (especially external specific surface area). Compared with HMCM-22, the HMCM-36 zeolites show lower acid amount; however, a larger amount of structurally accessible Brnsted acid sites located in the interlayer space of MCM-36 zeolites are exposed due to the formation of mesopores in the interlayer space, which should be favorable to the reaction involving bulky molecules.