Synthesis of LEV-type zeolite from aqueous nonalkaline fluoride aluminosilicate gels

Abstract

By using an original synthesis procedure in which the OH − ions are replaced by the F − anions as the mineralizing agent, the preparation of a LEV-type zeolite was possible from near-neutral nonalkaline reaction mixtures containing 1-azabicyclo[2.2.2]octane (quinuclidine) and optionally methylamine. The LEV-type zeolite could be synthesized only with a very narrow range of Si Al molar ratios in the framework, i.e., between about 8 and 11. The obtained products appear as ball-like aggregates of platelet crystallites. The samples were characterized through the usual techniques, e.g., XRD, STEM, d.t.a., and t.g.a., 13C, 29Si, 27Al, and 19F MAS n.m.r. spectroscopy. In the presence of quinuclidine alone, the occluded species is the quinuclidinium cation. In the presence of quinuclidine and methylamine simultaneously, a transformation reaction takes place during the synthesis, and the incorporated organic species are, besides the still preponderant quinuclidinium ion, the N-methylquinuclidinium ion and a cationic polymer identified as polyethylene piperidine. The low content of incorporated fluoride (0.3–0.6 wt%) corresponds to a variety of species, for instance to AIF to SiF groups, and also possibly to a F − ion trapped in the structure.