Silicalite-1 Growth from Clear Solution:  Effect of Alcohol Identity and Content on Growth Kinetics

Abstract

In situ small-angle X-ray scattering (SAXS) is used to investigate the influence of alcohol identity and content on silicalite-1 growth from clear solutions at 368 K. Several tetraalkyl orthosilicates (Si(OR)4, R = Me, Pr, and Bu) are used to synthesize silicalite-1 from clear solution mixtures comparable to those previously investigated (i.e. 1:0.36:20 TEOS:TPAOH:H2O (TEOS = tetraethyl orthosilicate; TPAOH = tetrapropylammonium hydroxide), 368 K). All TPAOH-organosiloxane mixtures studied form silica nanoparticles after aging at room temperature for 24 h. Full-profile fitting analysis of the SAXS data indicates the particles are ellipsoidal and is inconsistent with the presence of "nanoslabs" or "nanoblocks". Synthesis using TEOS as the silica source have an induction period of approximately 7.5 h and a growth rate of 1.90 +/- 0.10 nm/h at 368 K. Changing the silica source to tetramethyl orthosilicate (TMOS) does not change the induction period; however the particle growth rate is decreased to 1.65 +/- 0.09 nm/h at 368 K. Variable-temperature SAXS measurements for syntheses with TEOS and TMOS show the activation energy for silicalite-1 growth is 60.0 +/- 2.9 and 73.9 +/- 2.8 kJ/mol, respectively, indicating the alcohol identity does influence the growth rate. By mixing tetrapropyl orthosilicate (TPOS) with TEOS (1.6:1.0 molar ratio) as the silica source, the precursor solution shows a shorter induction period (6.0 h) and a faster particle growth rate (2.16 +/- 0.06 nm/h). The alcohol identity effect is more pronounced when other organocations (e.g. alkyltripropylammonium cations) are used to make silicalite-1 at 368 K. Removing ethanol from the precursor solution decreases the induction period to approximately 4.5 h and increases the particle growth rate to 2.99 +/- 0.13 nm/h. Mixtures with 2 equiv of ethanol have an induction period and particle growth rate of 6.0 h and 2.04 +/- 0.03 nm/h, respectively. The results demonstrate the alcohol identity and content influence silicalite-1 growth kinetics. One possible explanation is varying the alcohol identity and content changes the strength of the hydrophobic hydration of the structure-directing agent and the water-alcohol interaction, resulting in less efficient interchange between clathrated water molecules and solvated silicate species.

Few‐Unit‐Cell MFI Zeolite Synthesized using a Simple Di‐quaternary Ammonium Structure‐Directing Agent

“…6 h, 6 h and 48 h for Si‐FDP without EtOH, Al‐FDP and Sn‐FDP, respectively. EtOH and related alcohols could slow down crystallization as reported in a previous work [30] . For Si‐FDP, 24 h heating rendered almost fully crystalline products (Figure S18, a to d), while it took longer for Al‐FDP and Sn‐FDP, (Figure S18, e to h).…”

Growth kinetics of sulfur nanoparticles in aqueous surfactant solutions

“…4, is 0.60 ± 0.03 eV (57.65 ± 3.21 kJ/mol). It can be seen the activation energy of the coarsening process is low compare to the hydrophilic particles such as TiO 2 (72.35 kJ/mol) [21], ZnO (108.04 kJ/mol) [18] or silicalite-1 (73.90 ± 2.80 kJ/mol) [22]; as a result, there is a tendency to increasing particle size immediately after nucleation due to coarsening. The coarsening constant k c can be also written as,…”

Mechanism of crystallization of zeolite A microcrystals from initially clear aluminosilicate solution: A population balance analysis

“…13 and 14) indicate that the crystallization process generally takes place by a chain of processes: (i) formation of a small proportion of amorphous aluminosilicate at the very start of the crystallization process [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] (see also Fig. 1), (ii) formation of nuclei in the matrix of the amorphous aluminosilicate [13,[19][20][21][22]25,29,[40][41][42][43][44], (iii) release of nuclei from the matrix of amorphous aluminosilicate dissolved during the early stage of crystallization (autocatalytic nucleation [48,50,53,62,63,65,[70][71][72]), by the dynamics shown in Figs.…”

“…Hence, for a long time, a general meaning was that crystallization of zeolites from clear (alumino)silicate solutions takes place in a direct way, i.e., by nucleation and growth of zeolite crystals in/from the liquid phase [11,16,17], and thus without the formation of an intermediate amorphous (alumino)silicate. On the other hand, many recent studies of crystallization of different types of zeolites from clear (alumino)silicate solutions demonstrated the presence of (nano-scale) amorphous (alumino)silicate agglomerates formed during the room-temperature ageing [13,[18][19][20][21][22][23][24] or at the early stages of hydrothermal treatment of the synthesis solutions [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]. Formation and evolution of structurally ordered phase (potential nuclei) in the amorphous solids precipitated from initially clear (alumino)silicate solutions was evidenced by various experimental methods such as electron diffraction [13,40,41], highresolution transmission electron-microscopy [20][21][22]27], infrared spectroscopy [19][20][21][22], optical/electron-microscopy [42], small-angle X-ray scattering [25,29,…”

“…Formation and evolution of structurally ordered phase (potential nuclei) in the amorphous solids precipitated from initially clear (alumino)silicate solutions was evidenced by various experimental methods such as electron diffraction [13,40,41], highresolution transmission electron-microscopy [20][21][22]27], infrared spectroscopy [19][20][21][22], optical/electron-microscopy [42], small-angle X-ray scattering [25,29,43,44], wide-angle X-ray scattering [25,29] and small-angle neutron scattering [43]. However, although the formation of (nano-scale) amorphous aluminosilicate agglomerates in the starting clear (alumino)silicate synthesis solutions [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] and the formation of nuclei in the gel matrix are intensively researched and well documented in the appropriate publications [13,[19][20][21][22]25,29,[40][41][42]…”