Zeolite materials have complex structures that can be determined by X-ray diffraction (XRD), but characterizing the nonperiodic defects, the distribution of the aluminum atoms, and the position of the exchanged cations remain a challenge. It was shown that quantum chemistry methods (QMs) are well suited to predict the structure, even with low symmetry. Here, QMs were used to determine the location and coordination of Na-I and Cu-I cations in Si-rich faujasites of Y-type (with moderate Si/AI ratio) and Al-rich faujasites of X-type (Si/Al = 1). Focusing on the first shell of the metal site, we used QM analysis tools to study the various distortions induced by the presence of Al in the rings of faujasites. Such microscopic data were not accessible using experimental XRD methods. In contrast, using the present theoretical approach, it was possible to predict the absence of symmetry at the atomic level and that sites I were not occupied by Na-I nor by Cu-I cations, even for Al-rich faujasites of X-type. The infrared CO probe was used to analyze the interaction of both Na-I and Cu-I with the zeolite framework. Single CO adsorption on Na-I and Cu-I via the carbon atom showed that the calculated nu(CO) stretching frequency bands are mainly upshifted in comparison with isolated CO. The vco stretching frequency range was predicted to be larger for Cu-I than that for Na-I, and the bandwidth would be affected by different Al distributions in the six-membered rings (6MR): the more the Al atoms in the 6MR, the larger the bandwidth. To gain insights into the metal bonding picture with its neighbors, we performed natural bond orbital (NBO) analysis combined with the quantum theory of atoms in molecules and electron localization function topological analyses (QTAIM and ELF methods, respectively). While it is generally reported that Na cations provide electrostatic interactions with zeolite materials, Cu cations are often assumed to favor covalent interactions. The upshifting of the calculated nu(CO) stretching frequency and our topological analyses rather indicated that the interactions of Na-I and Cu-I with the oxygen atoms of the hosted zeolite were mainly ionic with a weak covalent character in the case of Cu-I. The adsorption of CO on Na-I proceeds via an ionic Na center dot center dot center dot C interaction, while for Cu-I, the Cu center dot center dot center dot CO bond was calculated to be dative with a strong polar character. Whatever the Lewis metal cation, Cu-I or Na-I, the present topological analyses predict that their interactions with the O atoms of the zeolite were ionic.

Boron heteroatom distributions are shown to be significantly different in two closely related layered borosilicates synthesized with subtly different alkylammonium surfactant species. The complicated order and disorder near framework boron sites in both borosilicates were characterized at the molecular level by using a combination of multi-dimensional solid-state nuclear magnetic resonance (NMR) spectroscopy techniques and first-principles calculations. Specifically, two-dimensional (2D) solid-state J-mediated (through-bond) (11)B{(29)Si} NMR analyses provide direct and local information on framework boron sites that are covalently bonded to silicon sites through bridging oxygen atoms. The resolution and identification of correlated signals from distinct (11)B-O-(29)Si site pairs reveal distinct distributions of boron heteroatoms in layered borosilicate frameworks synthesized with the different C16H33N(+)Me3 and C16H33N(+)Me2Et structure-directing surfactant species. The analyses establish that boron atoms are distributed non-selectively among different types of silicon sites in the layered C16H33N(+)Me3-directed borosilicate framework, whereas boron atoms are preferentially incorporated into incompletely condensed Q(3)-type sites in the C16H33N(+)Me2Et-directed borosilicate material. Interestingly, framework boron species appear to induce framework condensation of their next-nearest-neighbor silicon sites in the C16H33N(+)Me3-directed borosilicate. By comparison, the incorporation of boron atoms is found to preserve the topology of the C16H33N(+)Me2Et-directed borosilicate frameworks. The differences in boron site distributions and local boron-induced structural transformations for the two surfactant-directed borosilicates appear to be due to different extents of cross-linking of the siliceous frameworks. The molecular-level insights are supported by density functional theory (DFT) calculations, which show the distinct influences of boron atoms on the C16H33N(+)Me3- and C16H33N(+)Me2Et-directed borosilicate frameworks, consistent with the experimental observations.

Carbon monoxide is involved in many chemical and industrial processes, and its removal is of great importance to reduce detrimental environmental and climate impacts. CO is also useful to characterise the metal exchanged in zeolites. Multiple adsorption of CO in zeolite faujasites containing Na cations is investigated through quantum chemical calculations. Density functional theory (DFT) calculations were chosen to investigate the structure of sodium-exchanged cations at site II in Y faujasite and to investigate multiple CO adsorption with Na to predict the structure and the infrared CO stretching signal. DFT analysis using B3LYP, B3LYP-D and M062X showed significant differences in the coordination of Na at site II when three CO are adsorbed. From these investigations, polyadsorption of CO in NaY could lead to threefold-coordinated Na at site II in six-membered rings (6MRs) containing two Al and twofold-coordinated Na at site II in 6MRs containing one Al. These results suggest that introduction of non-bonding interactions is necessary to study polyadsorption of CO in NaY.

ADVERTISEMENT RETURN TO ISSUEPREVCommentNEXTComment on "A Computational Exploration of the CO Adsorption in Cation-Exchanged Faujasites"O. Cairon*View Author Information Chem. Des Pyrénées, 64160 Serres-Morlaàs, France*E-mail: [email protected]Cite this: J. Phys. Chem. C 2013, 117, 42, 22162–22164Publication Date (Web):September 25, 2013Publication History Received18 February 2013Revised9 September 2013Published online9 October 2013Published inissue 24 October 2013https://pubs.acs.org/doi/10.1021/jp401695khttps://doi.org/10.1021/jp401695karticle-commentaryACS PublicationsCopyright © 2013 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views343Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (166 KB) Get e-AlertscloseSUBJECTS:Adsorption,Cations,Fourier transform infrared spectroscopy,Metal clusters,Zeolites Get e-Alerts

Molecular simulations have been employed to explore at the microscopic. scale the adsorption of CO in two families of sodium exchanged faujasite, NaX and NaY. As a preliminary step, density functional theory calculations have been conducted to derive new sets of potential parameters for accurately describing the interactions between CO and the extra framework cations present within the supercage that act as preferential adsorption sites for the guest molecules. Two different parametrizations have been considered to discriminate the Na+ sites, Na-SII(+) and Na-SIII'(+), involved in the interactions with CO. On the basis of these forcefields, Grand Canonical Monte Carlo simulations were further realized to first predict the adsorption properties (isotherms and enthalpies) of these two types of faujasites up to high pressure. This was followed by a careful analysis of the microscopic mechanism in play along the whole adsorption process with a special emphasis on understanding the arrangements of CO in the vicinity of the Na+ whether they occupy SII or SIII' sites. These findings were discussed in light of the enthalpy profile obtained as a function of the loading and a. few experimental data available in the literature. Finally, complementary simulations were realized with mobile extra framework cations upon CO adsorption It was evidenced that Na-SII(+) can migrate toward SIII' sites in NaY, while in NaX, there is no cation redistribution within the supercage due to a steric hindrance. Such cation dynamics were shown to not drastically affect the adsorption properties of both Faujasites; however, this is a critical prerequisite to allow CO to form a double type interaction with both Na-SIII'(+) and Na-SII(+) via its C- and O-ends respectively, as predicted in cation exchanged zeolites using quantum chemical calculations.

We present a detailed investigation of the molecular structure of montmorillonite, an aluminosilicate clay with important applications in materials sciences, such as for catalysis, drug delivery, or as a waste barrier. Solid-state Si-29, Al-27, Mg-25, and H-1 nuclear magnetic resonance (NMR) measurements combined with density functional theory (DFT) calculations provide a comprehensive picture of the local structure and composition of a synthetic clay and its naturally occurring analogue. A revised composition is proposed based on NMR results that allow the identification and quantification of the signatures of otherwise undetectable noncrystalline impurities, thus largely complementing the traditional elemental analyses. Solid-state H-1 NMR at fast magic-angle spinning (MAS) and high magnetic field provide quantitative information on intra- and interlayer local environments that are crucial for the determination of the amount of Mg/Al substitution within the octahedral layer. In combination with DFT calculations of energies, it suggests that pairs of adjacent Mg atoms are unfavorable, leading to a nonrandom cationic distribution within the layers.

L'adsorption de CO dans la faujasite echangee au CuI et au Na+ a ete modelisee a l'aide des approches quantiques (DFT) et classiques (Monte Carlo). Grâce a l'approche DFT, la surface d'energie potentielle de la faujasite a ete exploree. Differents types d'interactions de CO avec les cations ont ete identifies, pour chacune les effets induits par l'adsorption de CO aux niveaux structural et energetique ont ete analyses, et le calcul de la frequence de vibration de CO a ete realise. Grâce aux valeurs obtenues, une nouvelle attribution des spectres d'adsorption de CO dans CuY et NaY a ete etablie. D'un autre cote, grâce aux simulations Monte Carlo dans l'ensemble Grand Canonique, les proprietes d'adsorption (isothermes et enthalpies) de la faujasite vis-a-vis de CO ont ete modelisees, et le mecanisme microscopique d'adsorption de CO a ete etabli. La mise en œuvre de ces simulations a necessite de parametrer un nouveau champ de force destine a decrire les interactions CO/faujasite et CO/CO.

CO adsorption in Al-rich latnasite zeolite containing copper and alkali cations has been investigated using DFT methods in order to determine how CO interacts and may modify the original position of the cations. Whether a cluster or a periodic model is used, addition of CO induces the formation of stable complexes labeled Dl((co)) in which CO interacts by both its C-end and its O-end, resulting from a coopperative rearrangement of cations. In addition to a Cu-1 migration from site II to the supercage. a migration of alkali from site III' to site Ill may occur, Dl((CO)) also induces a downshift of the no) mode in comparison with the complex containing CO interacting with a single cation, Slim,. These results suggest a new assignment of the IR spectra of CO adsorbed in YCu1 and YNa+: for YCu1, the upshifted signal at ca. 2160 cm(-1) in comparison with PCogas at 2143 cm(-1) could be assigned to a SI(CO) structure, whereas the downshifted signal it ca. 2140 cm(-1) could be assigned to a Dl((CO)) complex. For YNa+, the upshifted signal at ca. 2170 cm(-1) could be assigned to Na-sn center dot center dot center dot CO and/or to Dl((CO)) Na-SH center dot center dot center dot OC NasHr, whereas the downshifted signal at ca. 2122 cm(-1) could he assigned to Dl((CO)) compled Na-sn center dot center dot center dot CO center dot center dot center dot Na-SIH,Na- whereas the downshifted signal at ca. 2122 cm(-1) could be for understanding the metal-exchanged zeolite properties.