3D Study of the Morphology and Dynamics of Zeolite Nucleation

Abstract

The principle aspects and constraints of the dynamics and kinetics of zeolite nucleation in hydrogel systems are analyzed on the basis of a model Na-rich aluminosilicate system. A detailed time-series EMT-type zeolite crystallization study in the model hydrogel system was performed to elucidate the topological and temporal aspects of zeolite nucleation. A comprehensive set of analytical tools and methods was employed to analyze the gel evolution and complement the primary methods of transmission electron microscopy (TEM) and nuclear magnetic resonance (NMR) spectroscopy. TEM tomography reveals that the initial gel particles exhibit a core-shell structure. Zeolite nucleation is topologically limited to this shell structure and the kinetics of nucleation is controlled by the shell integrity. The induction period extends to the moment when the shell is consumed and the bulk solution can react with the core of the gel particles. These new findings, in particular the importance of the gel particle shell in zeolite nucleation, can be used to control the growth process and properties of zeolites formed in hydrogels.

Pioneering In Situ Recrystallization during Bead Milling: A Top-down Approach to Prepare Zeolite A Nanocrystals

“…In their bottom-up approach, Valtchev et al . carefully studied the crystallization kinetics under ambient temperature conditions, and proposed a mechanism for bottom-up formation, which views that the nucleation is initiated by an extensive exchange of species between solid and liquid phases during the induction period, and then crystal growth follows by an Ostwald ripening of the crystals 24 25 . However, in our opinion and from previous post-milling experiments, we postulate the following mechanism for the in situ recrystallization during bead milling.…”

Synthesis method for introducing mesoporosity in a faujasitic-like zeolite system from a sodium aluminosilicate gel composition

“…Even though CG 40 was amorphous by XRD, the electron micrograph (Figure 1b)shows bright spots. Such bright spots in the electron micrograph of an aluminosilicate gel has been related to trapped liquids in a study on EMT[27]. Since such spots were not observed in the case of RG, we propose an alternative explanation, that these bright spots are indicative of small crystalline The CG 20 sample crystallizes at 50 °C within 4 days.…”

Impact of the Zn source on the RSN-type zeolite formation

“…This diameter ranging from 2 to 4 nm is comparable with the dimensions of the smallest pores observed in TEM images as well as with the void size observed in EMT-type alumosilicate zeolite precursor. 35 Voids with similar size were detected even in the completely crystalline RUB-17. These voids most probably origiante from the texture of the agglomerated crystals.…”

“…Porous precursor gel particles have been found in many aluminosilicate zeolite yielding systems containing high concentrations of alkali cations. [35][36][37] The appearance and development of voids has been identified as an essential stage of the nucleation process and consequently crucial for the zeolite formation. As far as we know, this is the first report on the observation of voids within gel particles in zincosilicate precursors yielding a zeolite-type material.…”

“…[38][39][40] Melinte et al performed a very detail analysis of gel particles containing such voids and found that they contain shell which is impermeable for N2. 35 The majority of the mesopores exhibit diameter between 3 and 20 nm, more than 40% of the pores having a diameter between 5 and 7 nm. Consequently, any gas adsorption method could provide reliable information on the inherent porosity of the zeolite precursor samples due to the nonporous zone covering gel particles.…”