Accelerating the Crystallization of Zeolite SSZ‐13 with Polyamines

Abstract

Tailoring processes of nucleation and growth to achieve desired material properties is a pervasive challenge in synthetic crystallization. In systems where crystals form via nonclassical pathways, engineering materials often requires the controlled assembly and structural evolution of colloidal precursors. In this study, we examine zeolite SSZ‐13 crystallization and show that several polyquaternary amines function as efficient accelerants of nucleation, and, in selected cases, tune crystal size by orders of magnitude. Among the additives tested, polydiallyldimethylammonium (PDDA) was found to have the most pronounced impact on the kinetics of SSZ‐13 formation, leading to a 4‐fold reduction in crystallization time. Our findings also reveal that enhanced nucleation occurs at an optimal PDDA concentration where a combination of light‐scattering techniques demonstrate these conditions lead to polymer‐induced aggregation of amorphous precursors and the promotion of (alumino)silicate precipitation from the growth solution. Here, we show that relatively low concentrations of polymer additives can be used in unique ways to dramatically enhance SSZ‐13 crystallization rates, thereby improving the overall efficiency of zeolite synthesis.

Manipulation of amorphous precursors to enhance zeolite nucleation

“…Small particle size is also preserved at high PDDA coverage; however, it is likely that these conditions adversely impact the exchange of species between solid and solution states, thus leading to longer crystallization times. At C opt , it was observed by multiple light scattering techniques 60 that PDDA promotes the aggregation of precursors. We proposed a hypothesis that the solution within the interstitial spaces of the aggregated precursors promotes nucleation.…”

“…(D) Crystallization time of SSZ-13 in the absence (grey) and in the presence (blue) of PDDA at increasing polymer concentration (or PDDA/SiO 2 molar ratio). Data is taken from Dai et al60 with the shortest crystallization time at an optimal PDDA concentration (C opt ) around 0.2 wt% polymer (labelled with an arrow). (E) Cartoons illustrating how increased coverage of polymer on amorphous precursors with increasing polymer concentration putatively impacts the precursor-solution exchange, precursor aggregation, and the generation of confined interstitial pockets of solution between aggregated precursors at C opt 60.…”

“…Data is taken from Dai et al60 with the shortest crystallization time at an optimal PDDA concentration (C opt ) around 0.2 wt% polymer (labelled with an arrow). (E) Cartoons illustrating how increased coverage of polymer on amorphous precursors with increasing polymer concentration putatively impacts the precursor-solution exchange, precursor aggregation, and the generation of confined interstitial pockets of solution between aggregated precursors at C opt 60. Reproduced with permission from John Wiley and Sons, Inc. for images (A), (B) and (C) (copyright 2018).…”

“…The PDDA : SiO 2 molar ratios for MOR (6.0 Â 10 À6 ) and MFI (2.4 Â 10 À5 ) were determined by pre-screening for the optimal PDDA concentration (Fig.S9 †). The molar ratio used for CHA (1.2 Â 10 À5 ) was set equal to C opt in Fig.3D; however, experiments by Dai et al60 used fumed silica from a different vendor than the source used in this study, which accounts for differences in crystallization times. (B and C) High magnification scanning electron micrographs of the amorphous precursors extracted from a mordenite synthesis after 8 h of hydrothermal treatment using (B) FS/ PDDA and (C) FS-a/PDDA combinations.…”

Oxidative control over the morphology of Cu3(HHTP)2, a 2D conductive metal–organic framework

“…While the exact mechanism by which the oxidized HHTP polymer alters Cu 3 (HHTP) 2 morphology is not yet understood, macromolecular additives are well-known to inuence crystal formation. 30 For example, macromolecular additives have been shown to promote the nucleation of many crystal types, including small molecules and zeolites, 31,32 as well as modulate the growth of metal-organic frameworks. [33][34][35] Future work will focus on elucidating the structure of oxidized HHTP, and in situ studies to better understand how the polymer impacts nucleation and growth.…”