SYNTHESIS AND CHARACTERIZATION OF ZEOLITE NU-1 PREPARED FROM NEAR-NEUTRAL FLUORIDE ALUMINOSILICATE GELS

The preparation of zeolite Nu-1 from near-neutral (pH approximately 8- 10) fluoride containing media is difficult and only possible in a very narrow range of experimental conditions. Cocrystallization of other p hases (e.g., MTN-type and AST-type clathrasils and FER-type zeolite) i s often observed. Formation of pure Nu-1 could, nevertheless, be achie ved at 170-degrees-C in 5 d from a reaction mixture of the following m olar composition: 16.7 SiO2 : 1 Al2O3 : 0.5 Me4NCl : 1 NH4F : 9 H2O. T he ''crystals'' display a pseudocubic morphology, with, in some cases, a size up to 40 mum and consist, in fact, of small micrometric crysta llites. Zeolite Nu-1 was characterized by XRD, chemical analysis, ther mal analysis, and C-13, F-19, Al-27, and Si-29 MAS n.m.r. spectroscopy . Although the occluded organic species are mainly Me4N+ ions, some Me 3NH+ ions are also present. Three F-19 n.m.r. signals may be assigned to fluoride ions incorporated into the structure of zeolite Nu-1. Alth ough undetected by XRD, the presence of (NH4)3AlF6 as an impurity is s ystematically revealed by F-19 and Al-27 MAS n.m.r. spectroscopy.