孔壁含有沸石次级结构单元的MCM-48的合成及催化研究

孔壁含有沸石次级结构单元的MCM-48的合成及催化研究

  • 摘要: 以双表面活性剂(双极性头表面活性剂和三乙醇胺)为模板,以含有沸石次级结构单元的溶胶为前驱体,在碱性条件下合成了新型介孔分子筛MCM48。研究了沸石前驱体和三乙醇胺对产物MCM48形成的影响,XRD和TEM表征结果表明,样品具有较高的结晶度和规则的孔径;FTIR和N2吸附表征结果表明,产物MCM48的孔壁中含有沸石的次级结构单元,从而使得样品具有更大的比表面积。产物的重芳烃轻质化反应催化活性表明,实验样品对重芳烃的转化率比常规的MCM48高,转化率约高出11%,进一步证明了实验样品的孔壁中含有沸石的结构单元。

     

    Abstract: Mesoporous aluminosilicate MCM48 containing zeolite secondary building units in the pore wall, has been synthesized in alkaline media by a twostep procedure: the zeolite structure precursor was first synthesized by carefully controlling reaction conditions and then the presynthesized zeolite precursor was assembled using mixed templates of gemini surfactant \C18H37N(CH3)2(CH2)3N(CH3)2 C18H37\2+ and triethanolamine (TEA). Small angle XRD patterns of the asmade samples display strong diffraction peaks, indicating the highly ordered mesostructured MCM48 was formed. TEM images further show that the asmade sample has uniform cubic pore channel system with the pore diameter of about 2.5nm. FTIR technique was employed to characterize the pore wall of the MCM48 containing zeolite building units. IR spectra reveal an extra band at 520cm-1~600cm-1 assigned to fivemembered rings from zeolite structure, suggesting the presence of zeolite building units in the pore wall. N2 adsorption/desorption result shows the material has much higher specific surface area (1200m2/g), compared with the reported data (1100m2/g) of MCM48. This may be ascribed to the presence of micropores produced by zeolite secondary building units in its pore wall. The hydrogenation dealkylation reaction of heavy aromatic hydrocarbons on the asmade MCM48 catalyst gives higher conversion than that on traditional MCM48. Thus, it is concluded that asmade MCM48 containing the secondary building units of zeolites is of potential application in the catalytic conversion of large molecules. The key factors in our synthesis of MCM48 are the controlled preparation of zeolite precursor and the selection of auxiliary template.

     

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