Pressure-induced water intrusion in FER-type zeolites and the influence of extraframework species on structural deformations

doi:10.1016/j.micromeso.2014.02.036

Microporous and Mesoporous Materials

Volume 191, June 2014, Pages 27-37

https://doi.org/10.1016/j.micromeso.2014.02.036 Get rights and content

Highlights

•
Penetration of 15 water molecules in synthetic Si-FER compressed in m.e.w was found.
•
Eleven water molecules in the 10MR channels, forming bulk-like clusters.
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Four molecules were located in the FER cage as monodimensional clusters.
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Natural FER shows higher rigidity in m.e.w. and s.o. respect to the synthetic one.
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The presence of extraframework species in natural FER stiffens the structure.

Abstract

The response to pressure of a natural ferrierite from Monastir (Sardinia, Italy) (Mon-FER) and of the synthetic all-silica phase (Si-FER) was investigated by means of in situ synchrotron X-ray powder diffraction in the presence of penetrating (methanol:ethanol:water 16:3:1, m.e.w.) and non-penetrating (silicone oil, s.o.) pressure transmitting media (PTM). The following aspects are discussed: (i) the penetration of extra-H₂O molecules into the all-silica phase and the related structural aspects involving both framework and extraframework systems; (ii) the influence of the zeolite composition and of the different PTM used in the compression experiments on the overall elastic parameters of the two investigated samples; (iii) the elastic parameters and the unit cell P-induced deformations of the mineral phase; (iv) the reversibility extents of the observed phenomena. Evidence of H₂O molecules penetration during compression of Si-FER in m.e.w. was found. The refinement performed at 0.2 GPa enabled location of 15 H₂O molecules forming bulk-like and monodimensional H₂O clusters. No methanol or ethanol penetration was observed. The results demonstrate that the free volume of the porous material is not the only parameter influencing water condensation since applied pressure is an additional fundamental factor. The bulk modulus value calculated from P_amb to 4.9 GPa for Mon-FER (K₀ = 44 GPa, K_p = 0.2) is intermediate between the lowest (about 14 GPa) and the highest (about 72 GPa) values determined to date for zeolites compressed in non-penetrating PTM. The highest P-induced deformations are observed for Si-FER compressed in s.o. In general, higher rigidity for the natural sample was found in both media.

Graphical abstract

Introduction

Ferrierite (framework type FER, [1]) is both a well-known zeolite mineral [2], [3] and a synthetic porous material, prepared readily by both aqueous [4] and non-aqueous routes [5]. Its crystal structure [6], [7], [8] (Fig. 1a and b) is built up of rings of five SiO₄ tetrahedra (known as 5MR building units), which form layers on the ab plane. The layers are connected to form 10MR channels running parallel to [0 0 1], which are intersected by 8MR channels running parallel to the [0 1 0]. Six-membered rings connect the 10MRs channels along [0 1 0]. The structure contains cavities known as FER cages, formed by the intersection of the eight-membered ring channels and the six-membered ring channels (parallel to the c-axis).

An understanding of the stability and properties of ferrierite is of interest, beyond the mineralogical implications, because of the role of this porous material in many industrial processes. For example, it is used in the petrochemical industry as a shape selective catalyst for the production of isobutene [9]. In its Si-rich form, ferrierite has also been used for water purification [10], [11].

Ferrierite has been studied at high temperature (HT) by [12], working on the high silica form, while its high pressure (HP) behavior has never been investigated until now. In addition to HT, HP can also induce important structural changes in zeolites, modifying their physical and chemical properties and, consequently, their possible applications [13], [14]. It is well known that HP studies on porous materials can be performed using either penetrating or non-penetrating pressure-transmitting media (PTM). The former are usually aqueous/alcohol mixtures, with molecular sizes small enough to penetrate the zeolite porosities (see for example [15] and [16] for a review); the latter are usually silicone oil or glycerol, with molecules too large to penetrate the zeolite (see e.g. [14], [17], [18], [19], [20], [21], [22], [23], [24]). While non-penetrating PTM are mainly used to study zeolite compressibility, P-induced phase transitions, and amorphization, the penetrating ones can be usefully exploited for investigating the so-called pressure induced hydration (PIH) effect [25], which consists in the penetration of additional H₂O molecules into the zeolite channels. This phenomenon – which usually occurs from ambient conditions to about 3 GPa [16] – is particularly interesting in the case of irreversibility of the process upon P release, since, in this case, a new material of different composition and possibly different properties is produced. Moreover, understanding the changes in water structure as a consequence of the interactions with confining surfaces is of paramount interest for several technological applications (i.e. inhibition of corrosion, heterogeneous catalysis, design of super-hydrophobic surfaces, biological membranes, water purification) [26]. The interest in the confinement of water in nanoscopic spaces, like zeolitic cavities, stems from the fact that the properties of confined water are believed to be very different from those of the bulk fluid. Finally, it has been shown that the intrusion of extra-guest species into zeolite cavities also has important consequences on the overall elastic behavior of the material, since the new guest molecules generally contribute to stiffening the structure and countering P-induced deformations [18], [23], [24], [27], [28], [29].

In addition to PIH – occurring under pressure values of the order of GPa – another phenomenon has attracted renewed interest in recent years: water condensation in hydrophobic all-silica zeolites, a process that occurs within the pressure regime of the MPa see e.g. [30], [31], [32], [33]. In general, different behaviors can be observed, depending on various physical parameters of the matrix, such as pore size, pore system, channel dimensionality (one-, bi- or three-dimensional) [34], [35], [36], [37], and on the hydrophobic/hydrophilic character of the zeolite [33], [38]. According to the reversible or irreversible character of the intrusion–extrusion cycle, “water–Si-zeolite” systems are able to restore, absorb or dissipate mechanical energy. Consequently, molecular “spring”, “damper” or “shock-absorber” behavior can be observed [36], [37], [39], [40], [41], [42]. It must be noted, however, that none of these studies provided detailed structural information on “water–Si-zeolite” systems.

In this work the responses of two ferrierite samples to pressure in the presence of penetrating and non-penetrating PTM were studied: natural ferrierite from Monastir (Sardinia, Italy) (hereafter Mon-FER), and the synthetic all-silica phase (hereafter Si-FER). The following aspects will be discussed:

(i)
the penetration of extra-H₂O molecules into the all-silica phase and the related structural aspects involving both framework and extraframework systems;
(ii)
the influence of the zeolite composition and of the different PTM used in the compression experiments on the overall elastic behavior of the two investigated samples;
(iii)
the elastic parameters and the unit cell P-induced deformations of the mineral phase;
(iv)
the reversibility extents of the observed phenomena.

Section snippets

Experimental methods and data analysis

Mon-FER was chemically and physically characterized by Orlandi and Sabelli, [43] and by Alberti and Sabelli [7]. Its chemical formula is (Na_0.56K_1.19Mg_2.02Ca_0.52Sr_0.14)(Al_6.89Si_29.04)O₇₂·17.86 H₂O.

The synthetic Si-FER was synthesized following the synthesis procedure reported in [44]. The synthesized Si-FER was heat-treated for 72 h at 850 °C to remove the templates. The chemical composition was determined using a Cameca SX 50 electron microprobe on a pellet of the zeolite powder (experimental

Mon-FER

From Fig. 3a and b – which shows selected powder patterns of Mon-FER compressed in m.e.w. and s.o., respectively – it is evident that the peak intensity ratios change upon P increase. Moreover, while for the sample compressed in m.e.w. the peak profiles remain sharp, a marked peak broadening is observed for the patterns collected in s.o. In both experiments, ferrierite does not undergo complete amorphization and, upon pressure release, the features characteristic of the low P patterns are

Comparison between Mon-FER and Si-FER compressibility

Both experiments on Mon-FER reveal rather isotropic unit cell parameter variations upon compression. This is particularly evident in the experiment with s.o., while in m.e.w. a slightly higher contraction of the c parameter is observed above 1.8 GPa. Moreover, below this pressure value, compressibility in m.e.w. is lower than in the higher P regime. This can be ascribed to the entrance of some PTM molecules into the zeolite channels in the early stages of compression. This penetration is

Acknowledgements

The BM01 beamline at the European Synchrotron Radiation Facility is acknowledged for allocation of experimental beamtime. This work was supported by the Italian MIUR, within the framework of the following projects: PRIN2009 “Struttura, microstruttura e proprietà dei minerali”; PRIN2010-11 “Dalle materie prime del sistema Terra alle applicazioni tecnologiche: studi cristallochimici e strutturali”; FIRB, Futuro in Ricerca “Impose Pressure and Change Technology” (RBFR12CLQD).

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Pressure-induced water intrusion in FER-type zeolites and the influence of extraframework species on structural deformations

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Experimental methods and data analysis

Mon-FER

Comparison between Mon-FER and Si-FER compressibility

Acknowledgements

Zeolites

Catal. Today

Microporous Mesoporous Mater.

Microporous Mesoporous Mater.

Microporous Mesoporous Mater.

Microporous Mesoporous Mater.

Microporous Mesoporous Mater.

J. Solid State Chem.

J. Solid State Chem.

J. Colloid Interface Sci.

Microporous Mesoporous Mater.

C. R. Physique

Proc. 14th Int. Zeolite Conf.

Microporous Mesoporous Mater.

Mater. Res. Bull.

Atlas of Zeolite Framework Types

Natural Zeolites

Am. Mineral.

Nature

Acta Crystallogr.

Z. Kristallogr.

J. Am. Chem. Soc.

Ind. Eng. Chem. Res.

J. Am. Chem. Soc.

Am. Mineral.

Z. Kristallogr.