Zeolite Phase Selectivity Using the Same Organic Structure-Directing Agent in Fluoride and Hydroxide Media

Abstract

Force field-based calculations of all-silica zeolites show the role of fluoride as a structure-directing agent (SDA). Calculations of fully packed organic and fluoride SDAs were possible with an updated version of zeoTsda software, based on Monte Carlo+Lattice Energy Minimization. Comparison between fluoride-containing and fluoride-free calculations using the same organic SDA allowed us to predict which zeolite phase is obtained in fluoride and hydroxide media and also, through a new energy decomposition scheme, identify energetic contributions driving the synthesis outcome.

Different Zeolite Phases Obtained with the Same Organic Structure Directing Agent in the Presence and Absence of Aluminum: The Directing Role of Aluminum in the Synthesis of Zeolites

“…Further, the use of computational methods does not only allow us to compare the total energies and establish if the zeolite obtained is driven thermodynamically, as that with lowest energy, but also should allow us to calculate the different contributions to the energy and analyze which of them play a more dominant role in order to justify the phase obtained. Similar ideas have been recently used to computationally analyze the role of fluoride, by comparing synthesis routes that give different pure silica zeolites using the same OSDA in the absence/presence of fluoride . Among other results, this study suggests an explanation regarding the competition of pure silica UFI vs LTA when using 1,2-dimethyl-3-(2-fluorobenzyl)­imidazolium as an OSDA forming self-assembling dimers in the lta cavities present in both zeolites.…”

“…A detailed energy decomposition analysis was employed considering the various energy contributions to the total energy of the zeo–OSDA system for pure silica zeolites considering the hydroxide or fluoride route, depending on the synthesis (Table S1), using a similar strategy with one of our recent studies . The total energies of the zeo-SDA systems for pure silica zeolites can be calculated using the following expressions E normalz normale normalo − normalO normalS normalD normalA = E normalz normale normalo + E normalO normalS normalD normalA normalC normalo normalu normall ‐ normali normaln normalt normale normalr + E normalO normalS normalD normalA normalv normald normalw + E normalO normalS normalD normalA normali normaln normalt normalr normala + E normalz normale normalo − normalO normalS normalD normalA normalC normalo normalu normall ‐ normali normaln normalt normale normalr + E normalz normale normalo − normalO normalS normalD normalA normalv normald normalw E normalz normale normalo − normalO normalS normalD normalA ‐ normalF = E normalz normale normalo + E normalO ...…”

“…In this article, as well as in our recent previous study, 41 we introduce the idea of "competing phases" from a strict experimental viewpoint. As a consequence, the list of "competing zeolites" is obtained from all zeolites experimentally synthesized with a given OSDA, either as pure silica or as aluminosilicate.…”

A Review on the Effects of Organic Structure-Directing Agents on the Hydrothermal Synthesis and Physicochemical Properties of Zeolites

“…Finally, other factors such as amounts of trivalent atoms (e.g., Al), presence of other heteroatoms such as germanium, the H 2 O/Si molar ratio and the type of mineralizers (e.g., OH − , F − ) can influence the formation of certain crystalline structures. These factors become more pronounced if the SDA species are not fully matched within the porous network of a certain zeolitic structure [75,76]. For instance, gallosilicate ECR-34 with ETR topology (18-T atoms in one ring) is synthesized via collaboration between organic SDA and two inorganic cations (See Figure 4).…”

Theoretical design for zeolite synthesis

“…Later, they also showed that AEI, RTH, and CHA zeolites were successfully prepared from the design of organic templates that mimic the intermediates in MTO reaction [16]. For industrial applications of zeolites, it is strongly desirable to design lowcost templates for directing zeolite structures assisted with theoretical simulation [17][18][19][20][21][22][23][24][25][26]. Typical examples are the synthesis of SSZ-13, SSZ-52, and HPM-1 zeolites.…”