Could Mesophases Play a Role in the Nucleation and Polymorph Selection of Zeolites?

Abstract

Zeolites and mesoporous silicas are porous materials with important applications in catalysis, gas storage, and separation. Zeolite crystals form in the presence of cationic surfactants that act as structure directing agents (SDAs). The way SDAs control the nucleation and polymorphs selection in zeolites is not fully understood. The formation of mesoporous silica is templated by liquid crystalline mesophases that result from frustrated attraction between silicates and long-chain SDAs. Experiments indicate that surfactants C n H 2n+1 (CH 3 ) 3 N + with n > 6 yield mesoporous silicas, and the one with n = 6 produces a zeolite. This suggests that the driving force toward mesophase formation is also present for small organocations, but is overcome by the ability of silica to wrap a crystal lattice around them. Here we use molecular dynamics simulations to investigate whether the existence of metastable mesophases can play a role in the nucleation and polymorph selection of zeolitic crystals. As a proof of concept, we investigate the phase behavior of simple mesogenic mixtures of SDAs and a network former T that favors tetracoordinated crystals. We represent the network-former T by Stillinger−Weber models of water and silicon, in lieu of silica, because a computationally efficient silica potential that would allow for the spontaneous nucleation of zeolites in molecular dynamics simulations is not yet available. The mixtures of T and SDA produce a rich phase diagram that encompasses the sII clathrate and at least six zeolites, including sigma-2 (SGT). We find that the nucleation of SGT is not assisted by a mesophase. The nucleation of the other five zeolites of this study, however, is facilitated by the existence of metastable mesophases that decrease the nucleation barriers and direct the selection of the crystal polymorph. Together with the experimental support for mesophases in mixtures of silicates and SDAs, our results for model systems suggest that metastable mesophases could play a prominent role in promoting the nucleation and polymorph selection of some zeolites.

Ranking the Synthesizability of Hypothetical Zeolites with the Sorting Hat

“…This "Zeolite Sorting Hat" tackles data scarcity by using flexible and unbiased SOAP structural descriptors as inputs, and relatively simple and robust linear classification As it is the cases for many synthetic tasks, making zeolites is a form of art, guided by experience, chemical intuition and serendipity. The Zeolite Sorting Hat introduces datadriven techniques and rationale design [32,33] into the process of selecting candidates that we hope will accelerate the rate of discovery, which in turn will improve the predictive capabilities of the model in a positive feedback mechanism that will progressively take the guesswork out of zeolite synthesis.…”

Formation of hot ice caused by carbon nanobrushes

“…In a recent paper, Kumar et al suggested ways to find a new guest-free zeolitic ice: (1) incorporation of attractive guests, (2) application of pressure, and (3) relief of the strain in the water network via incorporation of other hydrogen-bonded molecules or ions. 51 Our approach can be classified in the first category. A solid surface of material can stabilize water and promote formation of zeolitic ices.…”

Twenty years of exceptional success: The molecular education and research consortium in undergraduate computational chemistry (MERCURY)

“…The faculty published 2 peer‐reviewed books, [ 238,239 ] 9 peer‐reviewed book chapters, [ 240–248 ] and 115 peer‐reviewed research papers. [ 249–363 ] This comes to 1.6 peer‐reviewed products/faculty/year during the 3‐year grant period, which is 3.2 times the rate of publication for natural science faculty at PUIs. [ 46 ]…”

“…One of the challenges to the overall undergraduate research movement is that the ability of undergraduate research to advance scientific knowledge remains undervalued. [ 364,365 ] From 2001, when the first NSF‐MRI grant was funded, through the summer of 2019, the MERCURY investigators have published 361 peer‐reviewed publications, including 2 in Chemical Society Reviews , [ 104,269 ] 1 in Chemical Reviews , [ 41 ] 1 in Nature Reviews Chemistry , [ 328 ] 3 in Science , [ 160,184,272 ] 2 in Nature , [ 271,344 ] 2 in Angewandte Chemie International Edition , [ 199,346 ] 13 in JACS , [ 20,24,26,36,59,71,84,112,136,169,289,315,336 ] and 3 in PNAS . [ 5,148,318 ] We published 44 papers during the first MRI grant period, [ 2–45 ] 50 during the second MRI grant period, [ 47–96 ] 62 during the third MRI grant period, [ …”