Adsorption by MFI-type zeolites examined by isothermal microcalorimetry and neutron diffraction. 1. Argon, krypton, and methane

Llewellyn, Philip L.; Coulomb, J.P.; Grillet, Y.; Patarin, Joël; Läuter, H.; Reichert, H.; Rouquérol, J.

doi:10.1021/la00031a036

Cited by 127 publications

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“…In fact, zeolite design for catalytic applications has also been inspired by the processes of molecular recognition characteristic of enzymes, 14 where solvation is an essential element. Experimental techniques such as FTIR and NMR spectroscopy, 15,16 or neutron scattering 17,18 provide very valuable information in this context, but if one desires a detailed three dimensional map of the confined fluid structure, the use of computer simulation is unavoidable. The calculation of density maps, particularly in regions where the sampling is poor due to problems of accessibility might turn into a computationally lengthy process.…”

Section: Introductionmentioning

confidence: 99%

A three dimensional integral equation approach for fluids under confinement: Argon in zeolites

Lomba

Bores

Sánchez-Gil

et al. 2015

The Journal of Chemical Physics

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In this work, we explore the ability of an inhomogeneous integral equation approach to provide a full three dimensional description of simple fluids under conditions of confinement in porous media. Explicitly, we will consider the case of argon adsorbed into silicalite-1, silicalite-2, and an all-silica analogue of faujasite, with a porous structure composed of linear (and zig-zag in the case of silicalite-1) channels of 5-8 Å diameter. The equation is based on the three dimensional Ornstein-Zernike approximation proposed by Beglov and Roux [J. Chem. Phys. 103, 360 (1995)] in combination with the use of an approximate fluid-fluid direct correlation function furnished by the replica Ornstein-Zernike equation with a hypernetted chain closure. Comparison with the results of grand canonical Monte Carlo/molecular dynamics simulations evidences that the theory provides an accurate description for the three dimensional density distribution of the adsorbed fluid, both at the level of density profiles and bidimensional density maps across representative sections of the porous material. In the case of very tight confinement (silicalite-1 and silicalite-2), solutions at low temperatures could not be found due to convergence difficulties, but for faujasite, which presents substantially larger channels, temperatures as low as 77 K are accessible to the integral equation. The overall results indicate that the theoretical approximation can be an excellent tool to characterize the microscopic adsorption behavior of porous materials. C 2015 AIP Publishing LLC. [http://dx

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Section: Introductionmentioning

confidence: 99%

A three dimensional integral equation approach for fluids under confinement: Argon in zeolites

Lomba

Bores

Sánchez-Gil

et al. 2015

The Journal of Chemical Physics

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“…Neutron and X-ray scattering techniques have been for years useful tools to gain a better understanding of adsorption processes [1][2][3][4][5] , very specially in order to locate active sites and/or privileged positions for the adsorption of certain adsorbates. Given the small ratio between adsorbate/adsorbent molecules, and since in many instances the adsorbent exhibits a well defined crystalline structure, one can expect a diffraction pattern that will be dominated by long range order features.…”

Section: Introductionmentioning

confidence: 99%

“…Those systems have been studied experimentally by Llewellyn and coworkers 2,15 and it is known that can reliably be modeled using GCMC simulations 15,16 . We will see how the proposed N-RMC approach, with the sole input of the relevant portion of the structure factor, the known zeolite structure, and an estimate of the number of adsorbate molecules per unit cell can accurately render the microscopic structure of the adsorbate in the course of a relatively short simulation run.…”

Section: Introductionmentioning

confidence: 99%

Reverse Monte Carlo modeling in confined systems

Sánchez-Gil

Noya

Lomba

2014

The Journal of Chemical Physics

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An extension of the well established Reverse Monte Carlo (RMC) method for modeling systems under close confinement has been developed. The method overcomes limitations induced by close confinement in systems such as fluids adsorbed in microporous materials. As a test of the method, we investigate a model system of 36 Ar adsorbed into two zeolites with significantly different pore sizes: Silicalite-I (a pure silica form of ZSM-5 zeolite, characterized by relatively narrow channels forming a 3D network) at partial and full loadings and siliceous Faujasite (which exhibits relatively wide channels and large cavities). The model systems are simulated using Grand Canonical Monte Carlo and, in each case, its structure factor is used as input for the proposed method, which shows a rapid convergence and yields an adsorbate microscopic structure in good agreement with that of the model system, even to the level of three body correlations, when these are induced by the confining media. The application to experimental systems is straightforward incorporating factors such as the experimental resolution and appropriate q-sampling, along the lines of previous experiences of RMC modeling of powder diffraction data including Bragg and diffuse scattering.

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“…Energetic and structural studies by means of Tian-Calvet isothermal microcalorimetry and neutron diffraction techniques further confirmed that the lowpressure hysteresis and associated energy changes were due to phase transition in the adsorbate. [16][17][18] …”

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confidence: 99%

“…[27] The first of these steps corresponds to localized adsorption at preferential high-energy sites, and the second to clustering around other adsorbed molecules. Taking into account the geometry of the pores, in addition to their size and the energetic or structural heterogeneity in ZSM-5 zeolite, a number of interesting features, even for other gas adsorption isotherms, can be observed for a series of MFI-type zeolites, [16,17,21,22,26,28,29] which differ from carbon molecular sieves. The orthorhombic ZSM-5 and Silicalite-I crystals have intersecting straight (along the [010] direction) and sinusoidal (zigzag) channels (along the [100] direction), [30] while the situation is quite different in the case of carbon molecular sieves, which have slit-shaped pores.…”

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Comment: Questions Concerning the Nitrogen Adsorption Data Analysis for Formation of Supermicropores in ZSM‐5 Zeolites

2005

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ZSM-5 zeolite has been of scientific and technological interest because of its diverse applications in heterogeneous catalysis, separation and purification, and lately in its environmental applications.[1] Although the well-defined micropores of ZSM-5 zeolite have excellent potential for chemical functions, the three-dimensional intersecting of sinusoidal and straight channels of molecular dimension often leads to diffusion limitations, limited accessibility, and a high back-pressure on flow systems.[2] Uniformly structured mesoporous molecular sieves are synthesized in such a way that a tunable pore size range of 2 to 30 nm can be achieved. However, as compared with conventional zeolites, the relatively weak acidity and poor hydrothermal properties of these invariably amorphous or paracrystalline materials severely hinder their practical applications.[3]Bridging the gap between microporous and mesoporous materials by developing materials of bimodal pore size distribution is thus currently a subject of interest. [4][5][6] Previous studies showed ZSM-5 zeolite with mesopores of diameter > ∼5 nm could be synthesized by templating with carbon materials, i.e., carbon black, carbon nanotubes, or carbon aerogels. [4][5][6] Our recent work showed that bimodal mesoporous ZSM-5 zeolites of tunable mesoporosities could be prepared using resorcinol-formaldehyde aerogels and carbon aerogels as templates. [7] However, crystalline structures containing pores in the size range 1.0-2.0 nm and exhibiting thermal and hydrothermal stability are highly desirable and have become a major challenge for the porous-materials community, especially if the pore system is more than one-dimensional, for example, tetrahedral frameworks containing extralarge pores in a multidimensional network.[8]Recently Yang et al. reported synthesis of a ZSM-5 zeolite with unique supermicropores using well-ordered mesoporous carbon (CMK-3) as a solid template.[9] The focus of that communication centered on hysteresis loops in the nitrogen adsorption/desorption isotherms at 77 K on ZSM-5 samples at a relative pressure P/P 0 (P and P 0 are the equilibrium pressure and saturation vapor pressure at the adsorption temperature, respectively) above 0.8 and/or hysteresis loops at P/P 0 ∼0.2. A hysteresis loop at P/P 0 above 0.8 is associated with the presence of large mesopores as a result of solid templating, which can be easily characterized with either scanning electron microscopy (SEM), transmission electron microscopy (TEM), or direct TEM stereoimaging as presented in previous contributions. [4][5][6]10] However a hysteresis loop at P/P 0 ∼0.2, ascribed to pore filling into supermicropores or small mesopores according to the analysis by Yang et al., [9] similar to that reported by Chen et al., [11] is not evident. The latter prepared an MFI-type zeolite that possessed a clear H1-type hysteresis loop at P/P 0 < 0.2 by structural transformation of CTA + -MCM-41, which was misinterpreted (for reasons to be given later) as capillary condensation characteristics cor...

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Adsorption by MFI-type zeolites examined by isothermal microcalorimetry and neutron diffraction. 1. Argon, krypton, and methane

Cited by 127 publications

References 0 publications

A three dimensional integral equation approach for fluids under confinement: Argon in zeolites

A three dimensional integral equation approach for fluids under confinement: Argon in zeolites

Reverse Monte Carlo modeling in confined systems

Comment: Questions Concerning the Nitrogen Adsorption Data Analysis for Formation of Supermicropores in ZSM‐5 Zeolites

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