Computational Screening of Structure-Directing Agents for the Synthesis of Pure Silica ITE Zeolite

This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry Letters, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.jpclett.0c01734.[EN] "Shape" was the first criterion claimed to explain the specificity between organic structure-directing agents (OSDAs) and zeolite micropores. With the advent of computational chemistry methods applied to study the effectiveness of SDA-zeolite combinations, "energy" (mainly van der Waals) became the most commonly invoked concept to explain the zeolite phase selectivity. The lower the energy, the better the SDA_ In this study, we rescue the concept of shape, and we combine it with the concept of energy within the frame of a SDA screening approach to identify new SDAs for the synthesis of cage-based ITE zeolite. Once we identify an appropriate shape fingerprint, filtering through the SDA database can be done quickly and accurately. With the shape selection, an automated Monte Carlo software allows us to assess the suitability using the force-field-calculated zeo-SDA energy. The computational approach can be promptly applied to other cage-based zeolites.We thank MICINN of Spain for funding through projects RTI2018-101784-B-I00, RTI2018-101033-B-I00, and SEV-2016-0683. S.L. thanks MICINN for the predoctoral grant BES-2017-081245 corresponding to project SEV-2016-068317-2. Prof. A. Corma is acknowledged for collaboration from the SEV-2016-0683 project. We thank ASIC-UPV for the use of their computational facilities.León-Rubio, S.; Sastre Navarro, GI. (2020). Computational Screening of Structure-Directing Agents for the Synthesis of Pure Silica ITE Zeolite. The Journal of Physical Chemistry Letters. 11(15):6164-6167. https://doi.org/10.1021/acs.jpclett.0c01734S616461671115Davis, M. E. (2013). 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The diffusion path reversibility confirms symmetry of surface barriers

The resistance perceived by guest molecules upon entering or leaving a microporous host material (the “surface barrier”) is known to often surpass the influence of diffusion in its interior on the overall rate of molecular uptake and release [1, 2]. Our knowledge of the relevant mechanisms of surface permeation, however, is still rather limited. This is related to the difficulties in its direct measurement which, given the “nanoscopic” extension of the relevant space scale, notably exceed the difficulties which do exist with already the diffusion measurement. A question discussed in this context refers to the possibility that the resistance perceived by the molecules on entering the pore space may differ from that perceived upon leaving [3-5]

Vibrational fingerprint of the absorption properties of UiO-type MOF materials

The absorption properties of UiO-type metal-organic frameworks are computed using TD-DFT simulations on the organic linkers. A set of nine isoreticular structures, including the UiO-66 and UiO-67 materials and functionalized variants, are examined. The excitation energies from a static geometry optimization are compared with dynamic averages obtained from sampling the ground-state potential energy surface using molecular dynamics. The vibrational modes that impact the excitation energy are identified. This analysis is done using a recently proposed tool based on power spectra of the velocities and the excitation energies. The applied procedure allows including important factors influencing the absorption spectra, such as the periodic framework, linker variation and dynamical effects including harmonic and anharmonic nuclear motions. This methodology allows investigating in detail the vibrational fingerprint of the excitation energy of advanced materials such as MOFs and gives perspectives to tailor materials toward new light-based applications

Carbonylation of dimethyl ether in mordenite using Inelastic Neutron Scattering

[EN] Zeolite mordenite (MOR, Si/Al =10) was used as catalyst for the reaction between CO and dimethyl ether (DME) to give methyl acetate. Since the reaction is catalysed by Bronsted acid sites, Inelastic Neutron Scattering (INS) is an appropriate technique to identify the intermediates. Although the accepted mechanism goes through an adsorbed methoxy, its characteristic peak at 963 cm-1 was only detected in the reaction MOR + DME, in the absence of CO. When CO is present, the peak at 963 cm-1 is substituted by other peaks that give valuable in-formation of the reaction intermediates, indicating that either methoxy intermediates are not formed or are quickly replaced by the acetyl intermediate, [SiO(COCH3)Al], strongly stabilised in the micropore pockets of mordenite. Upon reaction of MOR + CO + DME, a characteristic peak at 1050 cm-1, although being present in liquid methyl acetate, could not be assigned to adsorbed methyl acetate since it loses intensity as the reaction proceeds (upon heating), and was assigned to a strong interaction between CO and DME adsorbed in one or two Bronsted sites, leading to some intermediate that shares this vibrational feature with methyl acetate in liquid phase. Finally, a peak at 1275 cm-1 in the spectrum of MOR + CO + DME upon heating is assigned to the formation of methyl acetate when the sample is heated, corresponding to C-O stretching of methyl acetate. This is further confirmed by the absence of this peak before heating. Overall, INS technique has allowed an accurate determination and interpretation of peaks involved in the carbonylation of DME in mordenite.We thank CTI-CSIC for computational facilities. We thank ILL for neutron beam-time allocation (experiment 7-05-470). Financial support by the Spanish Ministry of Science and Innovation (CEX2021-001230-S grant funded by MCIN/AEI/10.13039/501100011033 funded by "ERDF A way of making Europe" and TED2021-130191B-C41 grant funded by the European Union NextGenerationEU/PRTR) are gratefully acknowledged. Authors thank also the financial support by Generalitat Valenciana (Prometeo 2021/077). This study forms part of the Advanced Materials programme and was supported by MCIN with partial funding from European Union Next Generation EU (PRTR-C17. I1) and by Generalitat Valenciana (MFA/2022/047).Jiménez-Ruiz, M.; Lemishko, T.; Rey Garcia, F.; Sastre Navarro, GI. (2024). Carbonylation of dimethyl ether in mordenite using Inelastic Neutron Scattering. Microporous and Mesoporous Materials. 364. https://doi.org/10.1016/j.micromeso.2023.11285036

Light olefin diffusion during the MTO process on H-SAPO-34 : a complex interplay of molecular factors

The methanol-to-olefins process over H-SAPO-34 is characterized by its high shape selectivity toward light olefins. The catalyst is a supramolecular system consisting of nanometer-sized inorganic cages, decorated by Bronsted acid sites, in which organic compounds, mostly methylated benzene species, are trapped. These hydrocarbon pool species are essential to catalyze the methanol conversion but may also clog the pores. As such, diffusion of ethene and propene plays an essential role in determining the ultimate product selectivity. Enhanced sampling molecular dynamics simulations based on either force fields or density functional theory are used to determine how molecular factors influence the diffusion of light olefins through the 8-ring windows of H-SAPO-34. Our simulations show that diffusion through the 8-ring in general is a hindered process, corresponding to a hopping event of the diffusing molecule between neighboring cages. The loading of different methanol, alkene, and aromatic species in the cages may substantially slow down or facilitate the diffusion process. The presence of Bronsted acid sites in the 8-ring enhances the diffusion process due to the formation of a favorable pi-complex host-guest interaction. Aromatic hydrocarbon pool species severely hinder the diffusion and their spatial distribution in the zeolite crystal may have a significant effect on the product selectivity. Herein, we unveil how molecular factors influence the diffusion of light olefins in a complex environment with confined hydrocarbon pool species, high olefin loadings, and the presence of acid sites by means of enhanced molecular dynamics simulations under operating conditions

Effect of Intracrystalline Silanol Defects on the Diffusivity of Benzene in Silicalite Zeolite

[EN] Intracrystalline zeolite silanol defect groups (& EQUIV;SiOH) were modelled in silicalite (silica ZSM-5, MFI) using experimental data. We make a molecular dynamics study on the self-diffusivity of benzene in silicalite with defects. The simulations at three different loadings (1, 3 and 5 benzene per unit cell) and temperatures (298, 348 and 398 K) allow to calculate self-diffusivity, adsorption energy and the activation energy. The results show that benzene self-diffusivity in silicalite is increased by the presence of silanol defects. Previous experimental results support this claim.This work was supported by Generalitat Valenciana predoctoral fellowship GRISOLIAP/2019/084. We also thank Generalitat Valenciana for funding through PROMETEO/2021/077 project and CESGA for the use of computational facilities. Financial support by the Ministry of Science and Innovation (MICINN) of Spain through project CEX2021-001230-S (10.13039/501100011033) is gratefully acknowledged.Misturini, A.; Altundal, ÖF.; García-Aznar, P.; Kariminasab, S.; Sastre Navarro, GI. (2023). Effect of Intracrystalline Silanol Defects on the Diffusivity of Benzene in Silicalite Zeolite. Chemie Ingenieur Technik. 95(11):1768-1776. https://doi.org/10.1002/cite.20230000817681776951

Separation of an aqueous mixture of 6-kestose/sucrose with zeolites: A molecular dynamics simulation

[EN] Extra-large pore zeolites are a small subset (21) among the whole list of 253 zeolites available. The discovery of new low-glycemic sugars is very attractive as new healthy additives in the food field. This is the case of the 6-kestose. In the present case, it appears in a mixture in aqueous solution together with sucrose, the separation of the mixture being necessary. For this, we have focused on using certain zeolites with adequate pore sizes that allow the separation of this mixture, considering that since the molecular size of 6-kestose is greater than sucrose, it is necessary to promote the sorption of the latter, so that the first can be purified. After a computational screening of micropores of the 253 IZA zeolites, 11 zeolites were selected. Of these, 3 extra-large pore zeolites (AET, DON, ETR) have been proposed, which were analyzed in-depth through a molecular dynamics study considering the external surface. The results show that DON presents the most promising theoretical results for a selective sucrose/6-kestose separation.We thank MICINN of Spain for funding through projects RTI2018101784-B-I00, RTI2018-101033-B-I00, SEV-2016-0683 as well as ASICUPV and CESGA for computational facilities. IBL and PGI gratefully acknowledge CSIC for a JAE-Intro fellowship. AM thanks Generalitat Valenciana for the predoctoral fellowship GRISOLIAP/2019/084.Bolaño Losada, I.; Grobas-Illobre, P.; Misturini, A.; Polaina, J.; Seminóvski, Y.; Sastre Navarro, GI. (2021). Separation of an aqueous mixture of 6-kestose/sucrose with zeolites: A molecular dynamics simulation. Microporous and Mesoporous Materials. 319:1-10. https://doi.org/10.1016/j.micromeso.2021.111031S11031

Isotopic H/D exchange on graphenes. A combined experimental and theoretical study

[EN] Adsorption of H-2/D-2 on graphene (G), graphene oxide (GO), single walled carbon nanotube (SWCNT), N-doped graphene [(N)G], and a sample of active carbon (C) has led to the detection of HD, indicating dissociative chemisorption of hydrogen on the surface of the material. The amount of HD detected follows the order G > SWCNT > GO similar to (N)G similar to C, G giving about five-fold higher H-2/D-2 adsorption and HD exchange level than SWCNT and about ten-fold larger values than that of the other samples. Quantum-chemistry calculations modeling a carbon atom vacancy on a G cluster estimates an activation barrier for H-2 dissociation of ca. 84 kJ/mol for a mechanism involving under coordinated carbon atoms at the defect site.Financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa SEV-2016-0267 and CTQ2015-69153-C2-R1) and Generalitat Valenciana (Prometeo 2013/014) is gratefully acknowledged. G. S. thanks the Scientific Division of SGAI CSIC for computing facilities.Sastre Navarro, GI.; Forneli Rubio, MA.; Almasan, V.; Parvulescu, VI.; García Gómez, H. (2017). Isotopic H/D exchange on graphenes. A combined experimental and theoretical study. Applied Catalysis A General. 547:52-59. https://doi.org/10.1016/j.apcata.2017.08.018S525954

Synthesis of High-Silica Erionite Driven by Computational Screening of Hypothetical Zeolites

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Chemistry of Materials, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.chemmater.9b01229.[EN] A hypothetical zeolite framework was selected from a database of hypothetical structures and adapted based on the structural features relevant for deNOx and MTO catalysis. To attempt the realization of this structure, a computational energy-based approach was applied to select relevant organic structure directing agent (OSDA) molecules with large OSDA-zeolite stabilization energies, leading to the selection of three OSDAs (OSDA1, OSDA2, and OSDA3) as potential candidates for the synthesis of the hypothetical zeolite (Hypo#1). Instead of Hypo#1, erionite (ERI) was found to dominate the experimental product outcome when potassium was used as a mineralizing agent. In the case of OSDA3, a novel high-silica ERI was found. The different ERI products were characterized, intergrowth structures ruled out, and special attention was paid to the compositional and morphological features arising from the use of the different OSDAs. In the specific high-Si product obtained using OSDA3, a distinct tubular to prismatic crystal morphology could be seen. Theoretical stabilization energies calculated for potentially competing phases (Hypo#1, ERI, offretite (OFF), and chabazite (CHA) among others) could be used to rationalize the experimental outcome to a certain extent, but our results also show that only considering zeolite-OSDA interaction is probably not sufficient to realize hypothetical frameworks, especially for Al-containing zeolites where alkali ions play an important role during crystallization.The authors thank Haldor Topsoe A/S and Innovation Fund Denmark for financial support under the Industrial PhD programe (case no. 1355-0174B). We thank MINECO of Spain for funding (SEV-2016-0683 and RTI2018-101033-B-100) and ASIC-UPV for the use of computational facilities. We also thank Prof. M. M. J. Treacy for assistance with the Database of Prospective Zeolite Structures.Boruntea, C.; Sastre Navarro, GI.; Lundegaard, LF.; Corma Canós, A.; Vennestrom, PNR. (2019). Synthesis of High-Silica Erionite Driven by Computational Screening of Hypothetical Zeolites. Chemistry of Materials. 31(22):9268-9276. https://doi.org/10.1021/acs.chemmater.9b01229S92689276312