First principles molecular dynamics calculation of the structure and acidity of a bulk zeolite

Campana, Luca; Selloni, Annabella; Weber, Jacques; Pasquarello, Alfredo; Pápai, Imre; Goursot, Annick

doi:10.1016/0009-2614(94)00731-4

Cited by 44 publications

(27 citation statements)

References 16 publications

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“…To include the effects of the zeolite framework on adsorption of C 2 H 4 in zeolites, a periodic electrostatic structure method can be utilized 28–31. This corresponds to the high loading case and is often computationally expensive for most zeolites due to their relatively large unit cells.…”

Section: Introductionmentioning

confidence: 99%

Theoretical study of the adsorption of ethylene on alkali‐exchanged zeolites

Ketrat¹,

Limtrakul²

2003

Int J of Quantum Chemistry

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ABSTRACT:The structures of alkali-exchanged faujasite (X-FAU, X ϭ Li ϩ or Na ϩ ion) and ZSM-5 (Li-ZSM-5) zeolites and their interactions with ethylene have been investigated by means of quantum cluster and embedded cluster approaches at the B3LYP/6-31G (d, p) level of theory. Inclusion of the Madelung potential from the zeolite framework has a significant effect on the structure and interaction energies of the adsorption complexes and leads to differentiation of different types of zeolites (ZSM-5 and FAU) that cannot be drawn from a typical quantum cluster model, H 3 SiO(X)Al(OH) 2 OSiH 3 . The Li-ZSM-5 zeolite is predicted to have a higher Lewis acidity and thus higher ethylene adsorption energy than the Li-FAU zeolites (16.4 vs. 14.4 kcal/mol), in good agreement with the known acidity trend of these two zeolites. On the other hand, the cluster models give virtually the same adsorption energies for both zeolite complexes (8.9 vs. 9.1 kcal/mol). For the larger cation-exchanged Na-FAU complex, the adsorption energy (11.6 kcal/mol) is predicted to be lower than that of Li-FAU zeolites, which compares well with the experimental estimate of about 9.6 kcal/ mol for ethylene adsorption on a less acidic Na-X zeolite.

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Section: Introductionmentioning

confidence: 99%

Theoretical study of the adsorption of ethylene on alkali‐exchanged zeolites

Ketrat¹,

Limtrakul²

2003

Int J of Quantum Chemistry

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“…26,27 Fast progress in both computer technology and the development of more efficient computer codes is pushing applications in two directions: ͑i͒ toward a still larger number of atoms in the unit cell, and ͑ii͒ toward time consuming applications of molecular dynamics. Typical extensions to large unit cells include the structural study of offretite ͑54 atoms/cell͒, 28,29 mordenite ͑144 atoms/cell͒, 30,31 and faujasite ͑576 atoms/cell͒. 32 Dynamical studies formerly focused to smallsize unit cells such as chabazite, 17 SAPO, 19,33 and sodalite 20,21,23 are now becoming feasible for medium sized cells, such as offretite.…”

Section: Introductionmentioning

confidence: 99%

Bro/nsted acid sites in gmelinite

Benco

Demuth

Häfner

et al. 1999

The Journal of Chemical Physics

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The structural properties of purely siliceous and Al-substituted protonated gmelinite, a zeolite with a medium-sized unit cell, are investigated by means of first-principles local-density functional calculations. For acid sites introduced into an Al-free structure, optimized geometries are compared with experimental data. The substitution of a Si–O fragment by Al–O–H induces a pronounced local deformation of the structure. Four symmetrically distinct O sites (O1–O4) are classified, according to the pattern of the deformation, into two categories showing rather localized (sites 2 and 3), and mostly delocalized (sites 1 and 4) distortions. Relative stabilities of protonated structures are shown to depend on the initial geometry of the site. Larger Si–O–Si angles lead to a higher stability of the acid site. Two approaches, a static and a dynamical one, are used to derive OH stretching frequencies. Both of them prove a rather complex relation between the infrared (IR) frequency, the acidity, and the local environment of the Bro/nsted acid site. The lowest OH stretching frequency is assigned to the O2 site as distinguished in the dynamical calculations. The shift occurs due to attractive interactions of H to the framework oxygen atoms.

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“…In this last case, the layers representing the solid are called a "slab". This approach has become highly popular since the 90's for the first principles simulation of zeolites, 20,103,[129][130][131][132] as the crystallographic structure of the latter is known, thus the initial content of the cell can be rather easily defined.…”

Section: Structural Modelsmentioning

confidence: 99%

Toward the Atomic Scale Simulation of Intricate Acidic Aluminosilicate Catalysts

Chizallet

2020

ACS Catal.

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Zeolites are nanoporous aluminosilicates with well-defined crystalline structures, considered key assets in heterogeneous catalysis, with a broad range of industrial applications. Computational investigations dealing with zeolite catalysts have been undertaken for decades with simple models of the bulk sites, known to be bridging Si IV −OH−Al IV groups, in the case where the compensation cation is a proton. Real zeolite catalysts used in practice are however finite size and intricate objects, with external surface sites and defects, among other sources of complexity. Amorphous silica−alumina may also be obtained as a consequence of zeolite post-treatments or synthesized on purpose to obtain acid sites that are milder than those of zeolites. In the present Perspective, some of the achievements in the field of the atomic-scale simulation of intricate aluminosilicate catalysts (zeolites, amorphous silica−aluminas) of industrial relevance are reviewed. Emphasis is put on the simulation of the mechanisms of post-treatments of zeolites, and on the special structure and reactivity of acid sites at external surfaces of zeolites and on amorphous silica−alumina, that is shown to differ from the properties of the bulk bridging sites. Moreover, directions for future investigations are proposed.

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First principles molecular dynamics calculation of the structure and acidity of a bulk zeolite

Cited by 44 publications

References 16 publications

Theoretical study of the adsorption of ethylene on alkali‐exchanged zeolites

Theoretical study of the adsorption of ethylene on alkali‐exchanged zeolites

Bro/nsted acid sites in gmelinite

Toward the Atomic Scale Simulation of Intricate Acidic Aluminosilicate Catalysts

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