Synthesis of borosilicate zeolites by the dry gel conversion method and their characterization

Borosilicate zeolites, [B]-BEA, [B]-MFI and [B]-MTW, were synthesized by th e dry gel conversion technique. Phase selection of the crystallization prod uct depended on the gel composition, mainly upon the SiO2/B2O3 and TEAOH/Si O2 ratio. Nearly complete conversion of gel to zeolites was achieved by thi s synthesis method, and there was no phase change during the crystallizatio n. It was observed from the C-13 CP MAS NMR of the as-synthesized samples t hat TEA(+) was fully intact in [B]-BEA, whereas partial decomposition of th e template occurred in [B]-MFI and [B]-MTW. FTIR and B-11 MAS NMR analyses of the samples indicated that boron was located mainly in the tetrahedral f ramework position. Most of the tetrahedral boron could be removed and subst ituted by repeatedly refluxing the calcined sample with aluminum nitrate so lution. (C) 1999 Elsevier Science B.V. All rights reserved.