Investigation of the physicochemical changes preceding zeolite nucleation in a sodium-rich aluminosilicate gel.

摘要: All industrially available zeolites are obtained from hydrogel systems. Unfortunately the level of understanding events preceding zeolite crystallization is far satisfactory. In this respect, revealing nature processes taking place in precursor gel paramount importance to nucleation. The investigation structure, however, a difficult task due complexity object terms both composition and topology. Therefore, combination hyperpolarized (HP) (129)Xe NMR-N(2) adsorption-high-resolution transmission electron microscopy-energy-dispersive spectrometry methods complemented by X-ray diffraction, infrared spectroscopy, scanning microscopy, chemical analyses has been employed study changes structure sodium hydroxide rich aluminosilicate yielding A. role each component system entire sequence during induction, nucleation, stages have revealed. high concentration studied found control size particles beginning stage. During initial polymerization species significant part expelled into solution, which restricts extensive leads formation small with open pore structure. induction period that follows marked incorporation Na back bulk gel. combined action ion as structure-directing agent hydroxyl group mobilizer results partial depolymerization voids mesopore sizes. nucleation maximum coincides temporally development pores sizes range 2-5 nm. amorphous undergoes crystalline only after these disappeared chemistry evolved reach stoichiometric composition. It was established unambiguously high-resolution microscopy HP NMR occurs solid succeeding commences nuclei released liquid, consistent autocatalytic mechanism. Also demonstrated unrivaled sensitivity capable identifying presence amounts material medium detection limit extending below 1 wt %.