SYNTHESIS OF BORON-BETA ZEOLITE FROM NEAR-NEUTRAL FLUORIDE-CONTAININGGELS

A borosilicate beta zeolite was prepared from almost neutral fluoride aqueous gels in the presence of 1,4-diazabicyclo [2.2.2]octane and met hylamine as the templates. The influence of several physical and chemi cal parameters was studied. In comparison with the (Si,Al) system, thi s (Si,B) system appears less 'reactive' with longer crystallization ti mes. Moreover, the products obtained display a narrower range of compo sitions. Only boron-rich (Si/B=2) and fluoride-poor media (F/Si=2) led to well-crystallized samples of beta zeolite characterized by a Si/B molar ratio close to 14. The differences observed between the two syst ems might be related to a stronger complexation of boron by the fluori de anions. The crystallization of the boron zeolite beta occurs probab ly through condensation reactions after hydrolysis of fluoroborate (BF 4-), hydroxyfluoroborate (BF3OH- and BF2(OH)(2)(-)) and fluorosilicate species. Zeolite beta was characterized by XRD, SEM, chemical analysi s, thermal analysis and B-11, F-19 and C-13 MAS NMR spectroscopy. The latter technique shows that the as-made beta samples contain, beside t he dabconium cation, a polymeric compound identified as polyethylene p iperazine. (C) 1997 Elsevier Science B.V.