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 the dry gel conversion technique. Phase selection of the crystallization product depended on the gel composition, mainly upon the SiO2/B2O3 and TEAOH/SiO2 ratio. Nearly complete conversion of gel to zeolites was achieved by this synthesis method, and there was no phase change during the crystallization. It was observed from the C-13 CP MAS NMR of the as-synthesized samples that TEA(+) was fully intact in [B]-BEA, whereas partial decomposition of the 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 framework position. Most of the tetrahedral boron could be removed and substituted by repeatedly refluxing the calcined sample with aluminum nitrate solution. (C) 1999 Elsevier Science B.V. All rights reserved.