具有b取向壳层MFI/MFI核壳分子筛的合成与表征

为了研究MFI/MFI核壳分子筛壳层b取向的形成机理，以圆柱形ZSM-5为核相，用碱性溶液对其表面预处理后，水热晶化合成具有高硅b取向壳层的MFI/MFI核壳分子筛，采用SEM、XRD、TEM、XPS和NMR等表征核相表面与晶化产物的结构。结果表明，核壳分子筛的（020）晶面衍射峰强度明显增强，壳层覆盖度为84％。核相碱处理是壳层形成的关键，未处理核相的表面上壳层不能生长，碱处理后在核相上形成的表面非骨架铝对高硅壳层颗粒的形貌和取向影响较大。在低铝含量条件下成核方式可能从非均相成核转变为均相成核，溶液中形成片状晶体，后经表面Si-OH强作用自组装得到二维紧密堆积的b取向壳层。

Synthesis and characterization of b-oriented MFI/MFI zeolite

In order to study the forming mechanism for b-oriented shell growth in MFI / MFI core / shell zeolite,the b-oriented MFI / MFI zeolite was synthesized by using alkaline pre-treated ZSM-5 crystals as the core material and hydrothermal crystallization method. The surface of the cores and the structure of core / shell product were characterized by means of SEM,XRD,TEM,XPS and NMR techniques. The results showed that the intensity of（ 020） diffraction peak for core / shell zeolite enhanced obviously,but the shell coverage was 84%,leaving some voids or defects on the external surface. The pre-treatment process was crucial to form the shell. The non-framework aluminum formed during the pre-treatment had great impact on the growth,orientation and shape of the shell crystal. A possible homogeneous nucleation process was induced under low non-framework aluminum condition. The b-oriented shell was obtained via crystal growth in solution to form lamellar crystals,and then following by self-assembly of these crystals onto the cores by Si-OH groups to produce two-dimensional close-packed layers.