Isomorphous substitution of boron

Hydrothermal Isomorphous Substitution of Boron in Zeolite ZSM—5/Silicalite... 

We report (i) isomorphous substitution of boron, by secondary synthesis, into silicalite and into highly siliceous (Si/Al>400) ZSM-5 and (ii) an improved direct synthesis of zeolite (Si,B) -ZSM-5. The chemical status of B in die boronated products depends upon reaction conditions. Careful control of the concentration of the base, the borate species and of die duration of treatment, allows the preparation of samples containing only 4-coordinated B or a mixture of 3- and 4-coordinated B in various relative concentrations. The products were characterized by magic-angle-spinning (MAS) NMR and infrared (IR) spectroscopies and by powder x-ray diffraction (XRD). 

We have earlier addressed the problem of the post-synthesis insertion of aluminium in zeolites ZSM-5 (12) and Y (Hamdan, H. Sulikowski, B. Klinowski, J. T.Phvs.Chem.. (in press)). The substitution of gallium in silicalite-n has also been achieved (13). It was therefore of considerable interest to establish whether boron can also be incorporated into silicate frameworks after the completion of synthesis. We report isomorphous substitution of boron into zeolite ZSM-5 by mild hydrothermal treatment with borate species. 

Isomorphous substitution of boron into the MFI structure to produce [B]ZSM-5 was carried out and investigated via FTIR micro-spectroscopy ( infrared microscopy ) of single crystals by Jansen et al. [308]. Typical bands were observed at 1380 and 905 cm. The integrated band intensity of the 905 cm" band was used as a quantitative measure of the boron content, and the boron distribution in the single crystals was shown to be homogeneous. 

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