Microporous and Mesoporous Materials 142 (2011) 696–707

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Microporous and Mesoporous Materials

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Elastic behavior of MFI-type zeolites: 1-Compressibility of Na-ZSM-5in penetrating and non-penetrating media

Rossella Arletti a, Giovanna Vezzalini b, Amine Morsli c, Francesco Di Renzo d, Vladimir Dmitriev e,Simona Quartieri f,⇑a Dipartimento di Scienze della Terra, Via Saragat 1, 44100 Ferrara, Italyb Dipartimento di Scienze della Terra, Via S. Eufemia 19, 41100 Modena, Italyc Département de Chimie, Université des Sciences et Technologie d’Oran, BP 1505 El Menaouar, Oran, Algeriad Institut Charles Gerhardt de Montpellier, UMR 5253 CNRS-UM2-ENSCM-UM1, 8 rue Ecole Normale, 34296 Montpellier, Francee Swiss–Norwegian Beam Line at ESRF, BP220, 38043 Grenoble Cedex, Francef Dipartimento di Scienze della Terra, Viale Ferdinando Stagno d’Alcontres 31, 98166 Messina S. Agata, Italy

a r t i c l e i n f o a b s t r a c t

Article history:Received 23 September 2010Received in revised form 13 January 2011Accepted 25 January 2011Available online 31 January 2011

Keywords:ZeoliteNa-ZSM-5High pressure structureElastic behaviorSynchrotron XRPD data

1387-1811/$ - see front matter � 2011 Elsevier Inc. Adoi:10.1016/j.micromeso.2011.01.022

⇑ Corresponding author. Tel.: +39 090 6765096.E-mail addresses: simona.quartieri@unimore.it, squ

We report the results of an in situ synchrotron X-ray powder diffraction study on the elastic behavior ofNa-ZSM-5, performed using both silicone oil (s.o.) and (16:3:1) methanol:ethanol:water (m.e.w.), as‘‘non-penetrating’’ and ‘‘penetrating’’ pressure transmitting media, respectively. In the range from ambi-ent pressure (Pamb) to 6.2 GPa, the reductions of a, b, c, and V observed in s.o. are: 6.4, 6.3, 6.9 and 18.5%,respectively. From Pamb to 7.4 GPa, a unit-cell volume reduction of about 14.6% is observed for Na-ZSM-5compressed in m.e.w., and the corresponding reductions of a, b, and c cell parameters are 6.3, 4.6, and4.5%, respectively. In both cases no phase transitions are observed and the unit cell parameters of ambi-ent conditions are recovered upon decompression. The complete structural refinements relative to theexperiments performed in m.e.w. up to 1.6 GPa reveal a strong increase in the extra-framework content– with the penetration of additional water/alcohols molecules in the partially occupied extra-frameworksites of as-synthesized Na-ZSM-5. This P-induced penetration, which does not induce any cell volumeexpansion, is only partially reversible, since a fraction of the extra-molecules remains in the channelsupon decompression. Our results show that Na-ZSM-5 is the softest microporous material among thoseso far compressed in s.o. Moreover, its compressibility is higher in s.o. than in m.e.w. (K0 = 18.2(6) GPa,K0 = 4 (fixed) and 28.9(5) GPa, K0 = 4 (fixed), respectively). This can be ascribed to the penetration ofthe extra-water/alcohol molecules, which contribute to stiffen the structure and to contrast the channeldeformations.

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1. Introduction

The behavior of zeolite materials under high temperatures hasbeen widely and profoundly investigated, due to the impact of thisthermodynamic parameter on their structures, stability, and con-sequently their applications [1–3]. More recently, it has been dem-onstrated that high pressure (HP) applied to microporous materialscan also induce important structural changes, which could modifythe physical properties and the accessibility of the zeolite catalyticsites for the molecular species entering the porous material. In theHP studies performed up to date on zeolites, either ‘‘pore penetrat-ing’’ (usually aqueous/alcohol mixtures; see, [4] for a review) or‘‘non-penetrating’’ P-transmitting media (usually silicone oil orglycerol; see, i.e. [5–8]) were used.

ll rights reserved.

artieri@unime.it (S. Quartieri).

The ‘‘penetrating’’ media are involved in the so-called pressure-induced hydration (PIH) phenomenon [9], which is characterizedby the penetration of additional water molecules into the zeolitechannels. This phenomenon is particularly interesting in case ofirreversibility upon P release, since, in this case, a new materialwith different composition and possible different properties is pro-duced. Although PIH usually occurs in a rather low pressure regime(from ambient conditions to about 3 GPa [4]), the behavior underhigher pressure values is usually followed to verify the baric stabil-ity of the material, the possible occurrence of new stable phasesand the reversibility/irreversibility of the process.

The studies performed with ‘‘non-penetrating’’ media high-lighted the crucial influence of the framework type and composi-tion and of the extra-framework content on the zeolite response,in terms of deformation mechanisms and compressibility values[7,10–12].

As part of a wide-ranging project aimed at investigatingthe compressibility behavior and HP stability of microporous

Fig. 1. (a) Projection of Na-ZSM-5 structure along [0 1 0], showing the straightchannels running parallel to the b axis; (b) (1 0 0) pentasil layer, showing theopenings of the sinusoidal channels running along the a axis. The labeled atoms areused to measure the channel openings (see text and Fig. 7).

Table 1Experimental and structural refinement parameters for the XRPD measurements insilicone oil (s.o.) and (16:3:1) methanol:ethanol:water (m.e.w.).

Experiment in s.o. Experiments in m.e.w.and at ambientconditions

k 0.7354 0.70026Detector MAR345 (pixel

dimension = 150 lm)MAR345 (pixeldimension = 150 lm)

Sample-detector distance(mm)

230 221

X-ray beam diameter(lm)

100 100

Exposure time (s) 300 180P-range (GPa) 0.3–8.1 0.1–7.4DP increment (GPa) 0.2–0.5 0.2–0.7Sample equilibration time

(min)30 30

Integration 2h range of thepowder patterns (�)

0–34 0–37

No. of coefficients used inthe Chebyshevpolynomial

22 20

R. Arletti et al. / Microporous and Mesoporous Materials 142 (2011) 696–707 697

materials, we are developing the study of the elastic behavior ofMFI-type zeolites [13] with different Si/Al ratios and differentextra-framework contents specifically: mutinaite, Na-ZSM-5, H-ZSM-5, and silicalite [14,15] compressed using both silicone oil(s.o.) and (16:3:1) methanol:ethanol:water (m.e.w.) as ‘‘non-penetrating’’ and ‘‘penetrating’’ pressure transmitting media,respectively. This paper reports the results for the response to HPof Na-ZSM-5 – properly synthesized and structurally characterizedfor this study – in in situ synchrotron X-ray powder diffraction(XRPD) experiments.

MFI-type zeolites have become extremely important as shape-selective industrial catalysts, due to their unique structure, consist-ing of intersecting channels formed by 10 (Al,Si)O4 tetrahedra[16,17]. The ‘‘straight channels’’ run parallel to the b axis whilethe ‘‘sinusoidal channels’’ run along the a axis. The window open-ings of these channels have a diameter of 5–6 Å, which enablescompounds of comparable size to enter and diffuse into the chan-nels (Fig. 1a and b). The maximum topological symmetry of MFIframework-type materials is orthorhombic Pnma, which is ob-served in as-synthesized ZSM-5. The extra-framework content,the nature and amount of Si substituents, and the temperaturehave been proved to influence the real symmetry of the materialand reduce the symmetry from orthorhombic Pnma to monoclinicP21/n space group (s.g.) [18,19]. In addition to the synthetic phases,a natural zeolite, mutinatite, has also been discovered to have theMFI topology, low Si/Al ratio, and s.g. Pnma [20].

Zeolites with MFI topology were originally synthesized in thepresence of a specific organic template (tetrapropylammoniumcation) [21] and presented as significant examples of the need oflarge cations to form zeolites with low aluminum content. It waslater realized that MFI-type zeolites can be formed in the presenceof a large variety of organic molecules [22]. The formation of Na-ZSM-5 in the absence of any organic molecule confuted establishedtheories and represented a major advance in the understanding ofzeolite properties [23,24]. At present, Na-ZSM-5 with a Si/Al ratioas high as 35, represents a significant share of the market of hydro-phobic adsorbents [25].

The specific aims of the present work are: (i) to investigate thestability, elastic behavior, and HP-structural evolution of Na-ZSM-5by means of in situ synchrotron XRPD, using both ‘‘penetrating’’and ‘‘non-penetrating’’ P-transmitting media; (ii) to verify the pos-sible capacity of Na-ZSM-5 to host additional molecules inside itsstructure; (iii) to establish the degree of reversibility of HP-inducedstructural modifications.

2. Experimental methods and data analysis

2.1. Synthesis procedure

Na-ZSM-5 was synthesized according to a published procedure[26]. The molar composition of the synthesis system was 5 Na2O/Al2O3/50 SiO2/3300 H2O. The reagents (NaOH from Prolabo, NaAlO2

from Carlo Erba, and precipitated silica Zeosil 175 MP from RhônePoulenc) were added to deionized water under stirring. The result-ing gel was stirred 4 h at room temperature, sealed in a stainlesssteel autoclave and heated 48 h at 170 �C in an oscillating device.The precipitate formed consisted in slightly inter-twined crystalsof ZSM-5. The crystal dimensions were measured after scanningelectron microscopy observations on a large number of specimensand resulted in these average values: 1.41 ± 0.42, 0.37 ± 0.06, and0.22 ± 0.08 lm, respectively in the directions of the axes c, a, and b.

2.2. Chemical analysis

Electron microprobe analysis was carried out using an ARL-SEMQ instrument in wavelength dispersive mode, operating at

15 kV and with a beam current of 20 nA and diameter of 30 lm;counting times of 5, 10, and 5 s. on high background, peak, and

Fig. 2. (a) Observed (crossed) and calculated (continuous line) diffraction patterns and final difference curve from Rietveld refinements of Na-ZSM-5 at ambient conditions.(b) and (c) Selected integrated powder patterns, collected in silicone oil and (16:3:1) methanol:ethanol:water, respectively, reported as a function of pressure. The patterns atthe top of the figures (labeled (rev)) were collected during decompression. (d) Observed (crossed) and calculated (continuous line) diffraction patterns and final differencecurve from Rietveld refinements at 1.6 GPa.

698 R. Arletti et al. / Microporous and Mesoporous Materials 142 (2011) 696–707

low background, respectively were used. A pellet of 10 mg of pow-dered Na-ZSM-5 sample was prepared by applying a pressure of10 tons m–2. The standards used were albite Amelia for Si and Na,microcline AB for K and Al, paracelsiane for Ba, anorthite for Sr,synthetic anorthite 70% for Ca, and olivine P140 for Mg and Fe.Data acquisition and processing were performed using the PROBE

program [27]. Water content was determined by thermogravimet-ric analysis on a 10 mg sample using a Seiko SSC/5200 instrument,operating at 5 �C/min from 18 to 800 �C in air. The weight loss was8.0%. The chemical formula calculated on the basis of 192 oxygenatoms and on the average of six point analyses is: (Na4.58 K0.02)(Ca0.18 Mg0.03 Ba0.01 Fe0.05 Sr0.01) (Si91.35 Al4.48) O192 28.39 H2O.

Table 2Unit-cell parameters of Na-ZSM-5 at the investigated pressures, using silicone oil(s.o.) and (16:3:1) methanol:ethanol:water (m.e.w.).

P (GPa) a (Å) b (Å) c (Å) V (Å3)

s.o.Pamb 20.1359(1) 19.904(1) 13.4363(9) 5385.1(4)0.3 20.082(1) 19.851(1) 13.399(1) 5341(1)0.5 20.013(2) 19.797(3) 13.357(3) 5292(2)0.7 19.951(2) 19.747(3) 13.309(3) 5243(2)0.9 19.838(3) 19.660(4) 13.217(3) 5155(2)1.2 19.798(4) 19.626(4) 13.193(3) 5126(2)1.3 19.716(4) 19.561(4) 13.131(4) 5064(3)1.8 19.590(5) 19.448(6) 13.039(5) 4968(3)2.1 19.484(6) 19.351(6) 12.953(5) 4884(3)2.5 19.457(7) 19.329(6) 12.940(6) 4867(4)2.9 19.357(6) 19.224(7) 12.862(6) 4786(4)3.3 19.298(8) 19.15 (1) 12.816(8) 4737(5)3.9 19.177(9) 19.02(1) 12.714(9) 4638(7)5.3 18.93(2) 18.75(2) 12.56(2) 4458(8)5.8 18.88(1) 18.68(1) 12.52(1) 4416(9)6.2 18.84(1) 18.64(2) 12.50(2) 4390(9)3.3 (rev) 18.91(2) 19.13(2) 12.83(2) 4642(10)Pamb (rev) 20.029(4) 19.856(5) 13.452(5) 5350(3)

m.e.w.Pamb 20.1359(1) 19.904(1) 13.4363(9) 5384.1(6)0.1 20.1067(5) 19.9246(6) 13.432(%) 5381.1(5)0.2 20.1007(7) 19.9196(8) 13.4288(7) 5376.8(5)0.3 20.0812(6) 19.9092(7) 13.4231(6) 5366.5(4)0.8 19.943(1) 19.85(1) 13.3773(9) 5295.9(6)1.0 19.9009(8) 19.8349(7) 13.3696(7) 5277.4(7)1.6 19.823(1) 19.7557(9) 13.3254(7) 5218.6(5)2.1 19.795(2) 19.736(2) 13.316(1) 5202.0(8)2.9 19.579(2) 19.535(2) 13.191(2) 5045(1)3.6 19.448(3) 19.427(3) 13.128(2) 4960(1)4.3 19.343(5) 19.324(4) 13.059(2) 4874(1)5.1 19.193(4) 19.244(3) 13.007(3) 4804(2)5.6 19.124(4) 19.159(5) 12.955(3) 4747(2)6.1 19.060(5) 19.102(5) 12.919(3) 4704(2)6.8 18.962(5) 19.016(6) 12.864(4) 4639(2)7.4 18.886(6) 18.956(6) 12.821(2) 4590(2)5.6 (rev) 19.102(5) 19.149(5) 12.947(4) 4736(2)3.3 (rev) 19.561(3) 19.538(3) 13.196(2) 5039(1)2.1 (rev) 19.763(3) 19.705(2) 13.295(1) 5177.3(8)1.2 (rev) 19.900(1) 19.859(1) 13.3808(9) 5288.1(6)Pamb (rev) 20.1649(9) 19.979(1) 13.4631(9) 5423.8(7)

Fig. 3. (a) Variation of Na-ZSM-5 lattice parameters as a function of pressuremeasured in silicone oil (s.o.). The errors associated with the cell parameters aresmaller than the symbol size. (b) Volume finite strain versus normalised stress plot(fe–Fe plot).

R. Arletti et al. / Microporous and Mesoporous Materials 142 (2011) 696–707 699

The balance error E% [28] is �10.31 for the average analysis; thisrather high value is due to the imperfect flatness of the samplesurface.

Fig. 4. Variation of Na-ZSM-5 lattice parameters as a function of pressure measuredin (16:3:1) methanol:ethanol:water (m.e.w.).

2.3. XRPD experiment at ambient pressure

Since, to the authors’ knowledge, no structural refinement of Na-ZSM-5 is available in the literature, it was necessary to perform adetailed study of the sample material under ambient conditions.The XRPD experiment at ambient pressure (Pamb) was performedat the SNBL1 (BM01a) beamline at ESRF, in the Debye–Scherrergeometry. The sample was placed in a 0.3 mm quartz capillarymounted on a goniometric spinning head and the diffraction pat-tern was collected. Table 1 reports some experimental parametersrelative to the measurements. Rietveld profile fitting was per-formed using the GSAS package [29], with the EXPGUI [30] inter-face. The powder pattern is reported in Fig. 2a. According to theextra-framework content and the Si/Al ratio value (equal to 20.4)of the sample, the s.g. is Pnma. The structure of mutinaite [20]was used as a starting model for the refinement since it gave thelowest R2

F value in the first cycle of the refinement. The backgroundcurve was fitted by a Chebyshew polynomial with an average of 20coefficients. The pseudo-Voigt profile function proposed byThomson et al. [31] was applied, and the peak intensity cut-offwas set to 0.5% of the peak maximum.

2.4. HP experiments in silicone oil and (16:3:1)methanol:ethanol:water

The HP synchrotron XRPD experiments were performed at theSNBL1 (BM01a) beamline at ESRF, with fixed wavelength of

Table 3Details of the four selected structural refinements of Na-ZSM-5 at Pamb, 0.3 GPa,1.2 GPa, and Pamb (rev).

Pamb 0.3 GPa 1.0 GPa Pamb (rev)

Rp 0.02 0.01 0.01 0.01Rwp 0.02 0.01 0.01 0.01

R2F

0.05 0.09 0.10 0.12

No. of variables 136 136 136 136No. of observations 2278 2229 2193 2214

Table 4Refined atomic positions and displacement parameters (Å2) of Na-ZSM-5 in m.e.w. at sele

Pamb

x/a y/b z/c Occ. Uiso

Si1 0.422(1) 0.062(1) 0.660(1) 1 0.017(1)Si2 0.315(1) 0.032(1) 0.817(1) 1 0.017(1)Si3 0.278(1) 0.061(1) 0.037(1) 1 0.017(1)Si4 0.120(1) 0.063(1) 0.031(1) 1 0.017(1)Si5 0.071(1) 0.028(1) 0.818(1) 1 0.017(1)Si6 0.188(1) 0.057(1) 0.683(1) 1 0.017(1)Si7 0.424(1) 0.8299(8) 0.681(1) 1 0.017(1)Si8 0.307(1) 0.875(1) 0.828(1) 1 0.017(1)Si9 0.276(1) 0.827(1) 0.042(1) 1 0.017(1)Si10 0.120(1) 0.825(1) 0.027(2) 1 0.017(1)Si11 0.069(1) 0.870(1) 0.818(2) 1 0.017(1)Si12 0.192(1) 0.825(9) 0.683(1) 1 0.017(1)O1 0.376(2) 0.067(2) 0.760(3) 1 0.026(2)O2 0.315(2) 0.041(2) �0.064(2) 1 0.026(2)O3 0.200(1) 0.070(2) 0.027(3) 1 0.026(2)O4 0.091(2) 0.063(2) �0.081(1) 1 0.026(2)O5 0.115(1) 0.063(2) 0.731(3) 1 0.026(2)O6 0.244(1) 0.047(3) 0.765(2) 1 0.026(2)O7 0.365(2) 0.849(3) 0.758(3) 1 0.026(2)O8 0.306(2) 0.839(2) �0.070(2) 1 0.026(2)O9 0.196(1) 0.838(1) 0.046(3) 1 0.026(2)O10 0.101(2) 0.843(2) �0.084(2) 1 0.026(2)O11 0.126(2) 0.850(2) 0.740(3) 1 0.026(2)O12 0.245(2) 0.842(3) 0.770(3) 1 0.026(2)O13 0.317(3) �0.046(1) 0.841(3) 1 0.026(2)O14 0.068(2) �0.052(1) 0.827(3) 1 0.026(2)O15 0.423(2) 0.134(1) 0.603(4) 1 0.026(2)O16 0.404(3) 0.004(1) 0.583(4) 1 0.026(2)O17 0.404(3) 0.866(2) 0.580(3) 1 0.026(2)O18 0.186(2) 0.114(1) 0.596(2) 1 0.026(2)O19 0.194(3) �0.009(1) 0.617(2) 1 0.026(2)O20 0.202(4) 0.866(1) 0.580(2) 1 0.026(2)O21 �0.003(1) 0.058(3) 0.801(3) 1 0.026(2)O22 �0.006(1) 0.857(3) 0.779(2) 1 0.026(2)O23 0.419(4) 0.75 0.663(6) 1 0.026(2)O24 0.170(3) 0.75 0.667(4) 1 0.026(2)O25 0.277(4) 0.75 0.080(4) 1 0.026(2)O26 0.106(4) 0.75 0.064(5) 1 0.026(2)X1 0.510(10) 0.25 0.945(10) 0.40(6) 0.035X2 0.511(4) 0.044(4) 0.039(6) 0.58(3) 0.035X3 0.551(4) 0.25 0.082(6) 0.72(6) 0.035X4 0.0313(30) 0.176(3) 0.623(5) 0.80(4) 0.035X5 0.449(3) 0.110(3) 0.886(5) 0.67(5) 0.035X6 1.000(5) 0.125(5) 0.435(7) 0.49(4) 0.035X7 0.297(4) 0.232(5) 0.831(5) 0.42(3) 0.035X8 0.168(4) 0.25 0.966(5) 0.79(4) 0.035X9 0.396(4) 0.25 0.891(6) 0.86(7) 0.035X10 0.104(2) 0.25 0.771(3) 1.4(6) 0.035X11 0.398(6) 0.163(6) 0.975(9) 0.36(4) 0.035X12 0.026(10) 0.25 0.875(10) 0.21(5) 0.035

1.0 GPa

x/a y/b z/c Occ. Uiso

Si1 0.422(1) 0.052(2) 0.655(2) 1 0.028(3)Si2 0.303(1) 0.030(1) 0.800(2) 1 0.028(3)Si3 0.281(1) 0.067(1) 0.028(2) 1 0.028(3)Si4 0.124(1) 0.059(1) 0.006(2) 1 0.028(3)Si5 0.071(1) 0.027(1) 0.801(2) 1 0.028(3)Si6 0.180(1) 0.061(1) 0.658(2) 1 0.028(3)

700 R. Arletti et al. / Microporous and Mesoporous Materials 142 (2011) 696–707

0.70 Å, using modified Merril-Bassett DACs [32]. Table 1 reportssome experimental parameters relative to the measurements per-formed in s.o. and m.e.w. Pressure was calibrated using the rubyfluorescence method [33] on the non-linear hydrostatic pressurescale [34]. The estimated precision in the pressure values is0.1 GPa. The experiments in s.o. were performed from 0.3 to8.1 GPa, while those in m.e.w. from 0.1 to 7.4 GPa. Some other pat-terns were collected upon decompression, from peak pressure toPamb. One-dimensional diffraction patterns were obtained by

cted pressures.

0.3 GPa

x/a y/b z/c Occ. Uiso

0.422(2) 0.052(2) 0.658(2) 1 0.020(1)0.3148(1) 0.032(1) 0.814(2) 1 0.020(1)0.277(1) 0.062(2) 0.040(2) 1 0.020(1)0.119(1) 0.068(1) 0.020(2) 1 0.020(1)0.075(2) 0.024(1) 0.808(2) 1 0.020(1)0.187(2) 0.060(1) 0.676(2) 1 0.020(1)0.425(2) 0.829(9) 0.677(2) 1 0.020(1)0.305(1) 0.875(1) 0.812(2) 1 0.020(1)0.280(1) 0.827(1) 0.036(2) 1 0.020(1)0.121(1) 0.830(8) 0.028(2) 1 0.020(1)0.067(1) 0.865(1) 0.813(2) 1 0.020(1)0.189(1) 0.826(1) 0.676(2) 1 0.020(1)0.379(2) 0.064(3) 0.759(3) 1 0.038(2)0.310(3) 0.055(3) �0.070(3) 1 0.038(2)0.199(1) 0.057(3) 0.020(3) 1 0.038(2)0.102(3) 0.0650(3) �0.098(2) 1 0.038(2)0.117(2) 0.071(2) 0.733(4) 1 0.038(2)0.253(2) 0.049(4) 0.740(3) 1 0.038(2)0.369(2) 0.842(3) 0.762(4) 1 0.038(2)0.296(3) 0.844(2) �0.080(2) 1 0.038(2)0.200(1) 0.832(2) 0.033(4) 1 0.038(2)0.085(3) 0.845(3) �0.075(2) 1 0.038(2)0.122(2) 0.835(3) 0.737(4) 1 0.038(2)0.237(2) 0.846(3) 0.766(3) 1 0.038(2)0.307(3) �0.046(1) 0.832(3) 1 0.038(2)0.063(3) �0.056(1) 0.801(3) 1 0.038(2)0.411(3) 0.128(2) 0.617(4) 1 0.038(2)0.398(3) 0.001(2) 0.574(3) 1 0.038(2)0.4087(3) 0.865(2) 0.575(3) 1 0.038(2)0.178(2) 0.128(2) 0.612(4) 1 0.038(2)0.191(3) �0.005(2) 0.607(3) 1 0.038(2)0.198(4) 0.865(2) 0.571(2) 1 0.038(2)-0.003(2) 0.043(4) 0.798(4) 1 0.038(2)-0.008(1) 0.858(3) 0.770(3) 1 0.038(2)0.406(4) 0.75 0.668(7) 1 0.038(2)0.171(3) 0.75 0.649(3) 1 0.038(2)0.286(5) 0.75 0.073(4) 1 0.038(2)0.110(5) 0.75 0.042(6) 1 0.038(2)0.426(6) 0.25 0.928(7) 0.52(5) 0.0350.516(2) 0.046(2) 0.002(4) 0.80(2) 0.0350.526(5) 0.25 0.085(8) 0.57(5) 0.0350.026(2) 0.189(3) 0.588(4) 0.69(3) 0.0350.434(2) 0.153(1) 0.893(4) 0.73(3) 0.0351.000(4) 0.142(2) 0.462(4) 0.62(3) 0.0350.311(6) 0.206(5) 0.873(7) 0.36(3) 0.0350.180(5) 0.25 0.920(5) 0.62(3) 0.0350.401(5) 0.25 0.784(6) 0.62(5) 0.0350.095(2) 0.25 0.761(3) 1.29(5) 0.0350.271(6) 0.257(21) 0.829(10) 0.26(3) 0.0350.0320(3) 0.25 0.882(3) 0.91(3) 0.035

Pamb (rev)

x/a y/b z/c Occ. Uiso

0.424(2) 0.056(2) 0.658(2) 1 0.023(2)0.316(2) 0.029(2) 0.816(3) 1 0.023(2)0.277(2) 0.063(2) 0.035(3) 1 0.023(2)0.119(2) 0.066(2) 0.026(3) 1 0.023(2)0.076(2) 0.027(2) 0.814(3) 1 0.023(2)0.192(2) 0.056(2) 0.677(3) 1 0.023(2)

Table 4 (continued)

1.0 GPa Pamb (rev)

x/a y/b z/c Occ. Uiso x/a y/b z/c Occ. Uiso

Si7 0.414(1) 0.830(6) 0.6580(2) 1 0.028(3) 0.423(2) 0.830(9) 0.679(2) 1 0.023(2)Si8 0.309(1) 0.872(1) 0.805(2) 1 0.028(3) 0.309(2) 0.873(2) 0.826(2) 1 0.023(2)Si9 0.278(2) 0.823(1) 0.024(2) 1 0.028(3) 0.279(2) 0.824(1) 0.044(2) 1 0.023(2)Si10 0.121(1) 0.827(1) 0.016(2) 1 0.028(3) 0.123(2) 0.829(1) 0.026(3) 1 0.023(2)Si11 0.066(1) 0.867(1) 0.807(2) 1 0.028(3) 0.069(2) 0.867(2) 0.811(3) 1 0.023(2)Si12 0.187(1) 0.824(1) 0.666(2) 1 0.028(3) 0.192(2) 0.825(1) 0.683(3) 1 0.023(2)O1 0.367(2) 0.063(3) 0.743(3) 1 0.033(3) 0.379(3) 0.061(3) 0.758(4) 1 0.013(4)O2 0.306(3) 0.058(3) �0.087(2) 1 0.033(3) 0.3120(3) 0.062(3) �0.072(3) 1 0.013(4)O3 0.204(1) 0.045(2) 0.016(3) 1 0.033(3) 0.199(2) 0.071(3) 0.025(4) 1 0.013(4)O4 0.098(2) 0.0710(2) �0.107(3) 1 0.033(3) 0.099(3) 0.067(3) �0.091(3) 1 0.013(4)O5 0.104(1) 0.062(3) 0.703(3) 1 0.033(3) 0.119(2) 0.064(3) 0.729(4) 1 0.013(4)O6 0.234(2) 0.048(4) 0.743(3) 1 0.033(3) 0.252(3) 0.051(5) 0.753(4) 1 0.013(4)O7 0.365(2) 0.826(2) 0.754(3) 1 0.033(3) 0.375(2) 0.848(4) 0.771(4) 1 0.013(4)O8 0.305(2) 0.858(2) �0.078(2) 1 0.033(3) 0.304(4) 0.836(2) �0.069(3) 1 0.013(4)O9 0.198(1) 0.840(2) 0.035(3) 1 0.033(3) 0.200(2) 0.840(2) 0.038(4) 1 0.013(4)O10 0.102(2) 0.833(2) �0.099(2) 1 0.033(3) 0.094(5) 0.848(3) �0.080(4) 1 0.013(4)O11 0.121(2) 0.849(2) 0.722(3) 1 0.033(3) 0.122(3) 0.832(3) 0.738(5) 1 0.013(4)O12 0.246(2) 0.843(3) 0.742(4) 1 0.033(3) 0.247(3) 0.846(4) 0.761(5) 1 0.013(4)O13 0.317(3) �0.049(1) 0.815(3) 1 0.033(3) 0.311(4) �0.048(2) 0.843(3) 1 0.013(4)O14 0.064(2) �0.054(1) 0.790(3) 1 0.033(3) 0.069(3) �0.053(2) 0.805(4) 1 0.013(4)O15 0.410(3) 0.122(2) 0.596(4) 1 0.033(3) 0.415(3) 0.130(2) 0.610(5) 1 0.013(4)O16 0.399(3) 0.009(2) 0.561(3) 1 0.033(3) 0.399(4) 0.003(2) 0.579(4) 1 0.013(4)O17 0.404(3) 0.873(2) 0.559(3) 1 0.033(3) 0.403(4) 0.864(2) 0.576(3) 1 0.013(4)O18 0.180(2) 0.133(2) 0.601(3) 1 0.033(3) 0.182(3) 0.117(2) 0.599(4) 1 0.013(4)O19 0.199(3) �0.005(2) 0.597(3) 1 0.033(3) 0.195(5) �0.012(2) 0.617(4) 1 0.013(4)O20 0.184(3) 0.864(2) 0.561(2) 1 0.033(3) 0.207(5) 0.866(3) 0.581(3) 1 0.013(4)O21 �0.008(2) 0.038(2) 0.785(3) 1 0.033(3) �0.003(2) 0.038(3) 0.798(5) 1 0.013(4)O22 �0.012(1) 0.8430(3) 0.798(4) 1 0.033(3) �0.002(2) 0.835(3) 0.780(4) 1 0.013(4)O23 0.412(3) 0.75 0.635(4) 1 0.033(3) 0.408(5) 0.75 0.684(6) 1 0.013(4)O24 0.158(3) 0.75 0.653(4) 1 0.033(3) 0.177(5) 0.75 0.651(4) 1 0.013(4)O25 0.299(3) 0.75 0.068(4) 1 0.033(3) 0.294(6) 0.75 0.088(5) 1 0.013(4)O26 0.112(4) 0.75 0.056(5) 1 0.033(3) 0.106(5) 0.75 0.039(8) 1 0.013(4)X1 0.492(7) 0.25 0.933(11) 0.42(7) 0.035X2 0.518(3) 0.064(4) �0.045(3) 0.54(2) 0.035 0.5 0 0 1.30(4) 0.035X3 0.528(2) 0.25 0.084(3) 1.38(4) 0.035 0.513(6) 0.25 0.022(8) 0.57(6) 0.035X4 0.039(3) 0.170(3) 0.557(5) 0.63(3) 0.035 0.044(4) 0.162(4) 0.623(7) 0.56(4) 0.035X5 0.443(2) 0.152(2) 0.911(3) 1.23(3) 0.035 0.449(2) 0.162(2) 0.902(5) 0.94(4) 0.035X6 1.015(2) 0.076(25) 0.389(4) 0.85(3) 0.035 1.010(4) 0.132(4) 0.423(5) 0.64(3) 0.035X7 0.356(1) 0.180(1) 0.88(1) 0.16(2) 0.035 0.298(6) 0.220(4) 0.794(5) 0.52(3) 0.035X8 0.1730(2) 0.25 0.903(2) 1.32(3) 0.035 0.245(4) 0.25 0.949(6) 0.74(5) 0.035X9 0.382(4) 0.25 0.814(5) 0.89(5) 0.035 0.393(4) 0.25 0.863(7) 1.04(7) 0.035X10 0.070(3) 0.25 0.716(3) 1.17(4) 0.035 0.105(3) 0.25 0.780(4) 1.51(6) 0.035X11 0.276(3) 0.275(3) 0.805(4) 0.63(2) 0.035X12 0.037(3) 0.25 0.869(3) 0.93(3) 0.035 0.031(4) 0.25 0.885(5) 0.72(4) 0.035

R. Arletti et al. / Microporous and Mesoporous Materials 142 (2011) 696–707 701

integrating the two dimensional images with the program FIT2D[35]. Selected integrated patterns are reported in Fig. 2b and c,for s.o. and m.e.w., respectively.

Unit cell parameters were determined by Rietveld profile fitting– using the GSAS package [29] with the EXPGUI [30] interface – upto 6.2 GPa in s.o. (the data quality of the higher pressure patternsbeing too low for refinement), and up to 7.4 GPa in m.e.w. Theinitial atomic coordinates were taken from the structural modelobtained from the Pamb experiment and based on mutinaite struc-tural data.

The background curves were fitted using a Chebyshev polyno-mial. The pseudo-Voigt profile function proposed by Thomsonet al. [31] and peak intensity cut-off were applied. The refined cellparameters as a function of pressure are reported in Table 2 and inFigs. 3a and 4 for s.o. and m.e.w., respectively.

The quality of the powder data collected in m.e.w. permittedcomplete structural refinements up to 1.6 GPa (see Fig. 2d). Thefollowing refinement strategy was used for Pamb and high pressurestructural refinements: (i) the scale factor, the zero-shift, and theunit cell parameters were allowed to vary for all refinement cycles(from the correlation matrix and from the almost constant value ofthe zero-shift resulting from each refinement step, we can rule outthe presence of significant correlation effects among zero-shift,

scale factor and the structural parameters); (ii) after the initialrefinement cycles, the refined structural parameters for each datahistogram were: fractional coordinates for all atoms (soft-restraints were applied to the T–O distances [Si–O = 1.60(2)–1.63(2)] and the weight was gradually decreased after the initialstages of refinement, down to a final weight of 10), occupancy fac-tors for extra-framework sites and thermal isotropic displacementfactors for all atoms (the isotropic displacement parameters wereconstrained in the following way: the same value for all tetrahedralcations, a second value for all framework O atoms, and a third va-lue for all the extra-framework sites); (iii) occupancy factors andisotropic thermal displacement factors for extra-framework siteswere varied in alternate cycles.

As discussed below, the starting coordinates of both frameworkand extra-framework sites of Na-ZSM-5 were taken from the struc-ture refinement of natural zeolite mutinaite. Notwithstandingmutinaite structural resolution was performed in the best availableexperimental conditions (on single-crystal and using synchrotronradiation), it was impossible to determine the precise chemicalcomposition (water or cations) of the extra-framework sites onthe basis of the distances between extra-framework sites andframework oxygen atoms. Hence, all the extra-framework siteswere refined with the oxygen scattering curve.

Table 5T–O framework distances (Å) for Na-ZSM-5 in m.e.w. at selected pressures.

Pamb 0.3 GPa 1.0 GPa Pamb (rev)

Si1– O1 1.623(8) 1.622(5) 1.623(5) 1.622(5)O15 1.612(8) 1.619(5) 1.621(5) 1.622(5)O16 1.592(8) 1.592(5) 1.590(5) 1.593(5)O21 1.613(8) 1.622(5) 1.620(5) 1.623(5)

Mean 1.610 1.614 1.614 1.615

Si2– O1 1.619(8) 1.622(5) 1.621(5) 1.623(5)O2 1.608(8) 1.622(5) 1.622(5) 1.620(5)O6 1.616(8) 1.624(5) 1.622(5) 1.622(5)O13 1.590(8) 1.594(5) 1.592(5) 1.593(5)

Mean 1.608 1.616 1.614 1.615

Si3– O2 1.614(8) 1.623(5) 1.622(5) 1.620(5)O3 1.587(8) 1.594(5) 1.590(5) 1.592(5)O19 1.591(8) 1.591(5) 1.591(5) 1.591(5)O20 1.594(8) 1.590(5) 1.591(5) 1.591(5)

Mean 1.596 1.600 1.599 1.599

Si4– O3 1.617(8) 1.624(5) 1.619(5) 1.622(5)O4 1.617(8) 1.622(5) 1.620(5) 1.591(5)O16 1.593(8) 1.591(5) 1.590(5) 1.593(5)O17 1.614(8) 1.621(5) 1.620(5) 1.621(5)

Mean 1.610 1.615 1.612 1.607

Si5– O4 1.581(8) 1.592(5) 1.590(5) 1.591(5)O5 1.613(8) 1.621(5) 1.621(5) 1.620(5)O14 1.613(8) 1.622(5) 1.623(5) 1.624(5)O21 1.610(8) 1.621(5) 1.620(5) 1.623(5)

Mean 1.604 1.614 1.614 1.615

Si6– O5 1.612(8) 1.622(5) 1.621(5) 1.620(5)O6 1.590(8) 1.593(5) 1.592(5) 1.590(5)O18 1.632(8) 1.62(5) 1.621(5) 1.621(5)O19 1.592(8) 1.591(5) 1.592(5) 1.591(5)

Mean 1.606 1.607 1.607 1.606

Si7– O7 1.615(8) 1.624(5) 1.622(5) 1.622(5)O17 1.587(8) 1.591(5) 1.590(5) 1.591(5)O22 1.612(8) 1.622(5) 1.617(5) 1.621(5)O23 1.612(8) 1.621(5) 1.621(5) 1.622(5)

Mean 1.606 1.615 1.613 1.614

Si8– O7 1.584(8) 1.595(5) 1.590(5) 1.593(5)O8 1.55(2) 1.589(5) 1.589(5) 1.590(5)O12 1.616(8) 1.621(5) 1.62(5) 1.622(5)O13 1.585(8) 1.592(5) 1.592(5) 1.592(5)

Mean 1.584 1.599 1.598 1.599

Si9– O8 1.634(8) 1.62(5) 1.621(5) 1.621(5)O9 1.618(8) 1.621(5) 1.619(5) 1.622(5)O18 1.586(8) 1.591(5) 1.590(5) 1.590(5)O25 1.613(8) 1.619(5) 1.619(5) 1.623(5)

Mean 1.613 1.613 1.612 1.614

Si10– O9 1.581(8) 1.591(5) 1.598(5) 1.591(5)O10 1.578(8) 1.59(5) 1.592(5) 1.591(5)O15 1.581(8) 1.589(5) 1.590(5) 1.591(5)O26 1.604(8) 1.619(5) 1.619(5) 1.620(5)

Mean 1.586 1.597 1.600 1.598

Si11– O10 1.56(2) 1.589 1.592(5) 1.590(5)O11 1.618(8) 1.620(5) 1.621(5) 1.621(5)O14 1.55(2) 1.590(5) 1.592(5) 1.594(5)O22 1.612(8) 1.620(5) 1.618(5) 1.621(5)

Mean 1.585 1.605 1.606 1.607

Si12– O11 1.592(8) 1.593(5) 1.591(5) 1.593(5)O12 1.62(2) 1.593(5) 1.591(5) 1.593(5)O20 1.625(8) 1.619(5) 1.621(5) 1.621(5)O24 1.576(8) 1.591(5) 1.591(5) 1.592(5)

Mean 1.603 1.599 1.599 1.600

702 R. Arletti et al. / Microporous and Mesoporous Materials 142 (2011) 696–707

Table 3 reports the details of four selected structural refine-ments at Pamb, 0.3 GPa, 1.0 GPa, and Pamb (rev), which will be dis-cussed below.

The isothermal bulk moduli of Na-ZSM-5 compressed in s.o. andm.e.w. were determined with the EOS-FIT program [36], using atruncated second-order Birch-Murnaghan equation of state [37].The elastic behavior along the axes was described with a ‘‘linear-ized’’ Murnaghan equation of state [38].

3. Results and discussion

From Fig. 2b and c it is evident that, for both experiments, thepeak intensities of the powder patterns decrease and the peak pro-files become broader with increasing pressure. This is especiallyevident in the patterns collected in s.o. Contrary to that observedupon heating [19], Na-ZSM-5 does not undergo HP-induced phasetransitions up to the highest investigated pressures. As discussedbelow in more detail, the features present in the patterns collectedat low pressure in m.e.w. are reversibly regained upon decompres-sion from HP, while the reversibility is only partial for the spectracollected in s.o.

3.1. Elastic behavior in silicone oil

As previously discussed, Na-ZSM-5 was compressed in s.o. up to8.1 GPa, but the unit cell parameters were successfully refined onlyup to 6.2 GPa. In this P-range, the reductions of a, b, c, and V are:6.4, 6.3, 6.9, and 18.5%, respectively (Table 2 and Fig. 3a). The unitcell parameters of the Pamb pattern are recovered well upondecompression, but a small hysteresis effect is observed at3.3 GPa (rev), in particular for the a axis. On the contrary, the Pamb

peak intensities are only partially recovered (Fig. 2b).Fig. 3b, which reports the Eulerian strain (fe) versus ‘‘norma-

lised pressure’’ (Fe) plot (fe–Fe plot; fe = [(V0/V)2/3 � 1]/2; Fe = P/[3f(1 + 2f)5/2]), indicates that the elastic behavior of Na-ZSM-5can be described with a second-order Birch–Murnaghan equationof state [37]. The elastic parameters, obtained using the dataweighted by the uncertainties in P and V, are V0 = 5413(7) Å3,K0 = 18.2(6) GPa, K0 = 4 (fixed). The refined linear axial bulk moduliare: K0(a) = 19.6(5); K0(b) = 20.4(3); K0(c) = 16.5(5) for the a, b, andc-axis, respectively. Since the bulk modulus values determined forzeolites compressed in ‘‘non-penetrating’’ P-transmitting mediarange from 19 (for triclinic analcime) to 72 GPa (for Li-ABW) [7],Na-ZSM-5 can be classified as the most compressible alumino-silicatic zeolite studied to date under these conditions, amongwhich zeolite A, Na-X, faujasite, heulandite, gismondine, yugaw-aralite and fibrous zeolites.

3.2. Elastic behavior in m.e.w.

From Pamb to 7.4 GPa a unit-cell volume reduction of about14.6% is observed for Na-ZSM-5 compressed in m.e.w., while theunit cell axes undergo the following reductions: Da = 6.3,Db = 4.6, Dc = 4.5% (Table 2 and Fig. 4a and b). These data clearlyshow that the P-induced effects in s.o. and m.e.w. are different,with a more ‘‘rigid’’ and less isotropic behavior of the microporousmaterial when compressed in m.e.w. Moreover, under these condi-tions, the most compressible axis is not c – as observed in s.o. – buta. This suggests that the use of different P-transmitting media in-duces rather different compression mechanisms in Na-ZSM-5.

The lower compressibility of Na-ZSM-5 in m.e.w. with respectto s.o. is in agreement with the behavior of other zeolites studiedwith both media (see e.g. the recent papers on Li-ABW [6] andboggsite [8]) and suggests the possible penetration of additionalhost molecules into the pores, which, due to the channel dimen-sions of Na-ZSM-5, could be in principle both water and alcohol

molecules. As discussed in detail below, the penetration of addi-tional water/alcohol molecules has been confirmed by the com-plete structural refinements performed between Pamb and1.6 GPa, which demonstrated a variation in the composition ofthe extraframework system.

Due to the penetration of additional extra-framework species,and the consequent change of the chemical composition of the

Table 6Interatomic distances (<3.20 Å) of the extraframework population for selected refinements of Na-ZSM-5 in m.e.w.

Pamb 0.3 GPa 1.0 GPa Pamb (rev)

X1– X3 2.01(22) 2.91(11) 1.27(15)X4 1.78(12) x2 2.37(11) x2 2.18(12) x2X5 3.14(12) x2 2.00(7) x2 2.00(13) x2X6 2.97(13) x2 3.01(9) x2 3.07(12) x2X7 2.57(15) x2X8 2.41(21)X9 2.00(9) 2.20(16)X11 2.88(20) x2

X2– O5 2.65(4)X2 2.08(16) 1.94(8) 3.12(14)X4 3.09(7) 1.99(10)X5 2.74(10) 3.06(7) 2.37(7)X6 1.67(13) 2.00(7) 3.04(7) 2.85(7) x2X6 2.10(5)

X3– X1 2.01(22) 2.91(11) 1.27(15)X4 3.14(8) x2 2.62(9) x2 2.42(7) x2 2.70(10) x2X5 2.71(11) x2X6 2.70(10) x2 2.29(6) x2 2.46(8) x2

X4– O5 3.13(6) 3.16(5) 2.86(9)O18 2.93(5) 2.95(7)X1 1.78(12) 2.37(11) 2.18(12)X2 3.09(7) 2.13(10)X3 3.14(8) 2.62(9) 2.48(7) 2.70(10)X4 2.94(11) 2.48(11)X5 2.12(7) 2.00(7) 1.98(6) 1.93(7)X6 2.80(12) 2.00(9) 2.96(7) 2.83(11)X8 3.11(9)X10 2.88(7) 2.96(5) 2.72(6) 3.03(9)X11 3.01(13)

X5– O1 2.39(7) 2.75(4) 3.14(6)O2 3.02(6) 3.12(4)O21 2.90(7)X1 3.14(12) 2.00(7) 2.00(10)X2 2.74(10) 3.06(7) 2.36(7)X3 2.71(11)X4 2.12(7) 2.00(7) 1.98(6) 1.93(7)X6 2.63(11) 2.37(7) 2.71(11)X7 2.70(11) 1.92(21)X8 2.98(6)X9 2.52(8) 2.63(5) 2.16(6)X11 1.89(11)

X6– O7 3.11(8)O14 2.90(4)O22 2.86(8) 3.12(5) 3.00(4) 2.80(7)X1 2.97(13) 3.01(9) 3.07(12)X2 1.67(13) 2.01(7) 2.99(7) 2.85(7)X2 2.10(5)X3 2.70(10) 2.29(6) 2.46(8)X4 2.80(12) 2.00(7) 2.96(7) 2.83(11)X5 2.63(11) 2.37(7) 2.71(8)X11 2.50(16)

X7– O1 3.01(22)O2 3.08(9) 2.62(21)O20 3.02(9) 2.63(19)X1 2.57(15)X5 2.70(11) 1.92(21)X7 0.73(20) 1.75(19) 2.76(4) 1.20(16)X8 3.19(12)X8 2.178(21) 2.85(14) 2.417(11)X9 2.34(13) 1.77(19) 2.22(10)X11 3.13(14) 1.43(20) 2.64(12)X11 1.24(18) 2.03(21)

X8– O17 3.10(5) x2O20 3.10(5) X2O24 3.14(8)X7 3.19(12) x2 2.85(14) x2 2.41(11)X10 2.91(8) 2.73(8)X11 2.21(15) x2 2.49(6) x2X12 3.12(27) 3.01(12) 2.73(7)

X9– X1 2.41(21) 2.00(7) 2.20(16)X3 3.06(11)X4 3.11(9) x2

(continued on next page)

R. Arletti et al. / Microporous and Mesoporous Materials 142 (2011) 696–707 703

Table 6 (continued)

Pamb 0.3 GPa 1.0 GPa Pamb (rev)

X5 2.98(6) x2 2.52(8) x2 2.63(5) x2 2.16(6) X2X7 2.178(21) x2 2.34(13) x2 1.77(19) x2 2.22(10) X2X11 2.07(13) x2 2.69(14) x2 2.18(7) x2

X10– X4 2.88(7) x2 2.96(5) x2 2.72(6) X2 3.03(9) X2X8 2.91(8) 2.76(8)X12 2.092(21) 2.05(7) 2.15(5) 2.05(13)

X11– O2 2.90(12)O20 2.49(12)X1 2.88(20)X4 3.01(13)X5 1.89(11)X6 2.50(16)X7 3.13(14) 1.43(20) 2.64(22)X7 1.24(28) 2.03(21)X8 2.07(13) 2.21(15) 2.49(6)X9 2.69(14) 2.17(7)X11 0.3(8) 1.02(13)

X12– O15 3.18(11) x2O26 2.78(13) 3.01(5) 3.11(7) 2.95(6)X8 3.12(27) 3.01(12) 2.73(7)X10 2.09(2) 2.05(7) 2.15(5) 2.05(13)

704 R. Arletti et al. / Microporous and Mesoporous Materials 142 (2011) 696–707

material, the elastic parameters of Na-ZSM-5 were calculated afterthe second discontinuity (that is between 2.9 and 7.4 GPa). Using atruncated second-order Birch–Murnaghan equation of state andthe data weighted by the uncertainties in P and V, the following re-sults were obtained: V0 = 5500(10) Å3, K0 = 28.9 (5) GPa, K0 = 4(fixed). The refined linear axial bulk moduli are: K0(a) = 21.2(5);K0(b) = 33.0(8); K0(c) = 33.1(10) for the a, b, and c-axis, respec-tively. Although the compressibility determined in m.e.w. is lowerthan in s.o., it is still one of the highest when compared with othernatural and synthetic zeolites studied with ‘‘penetrating’’ aqueousmedia [4].

Fig. 5. Projection of the Na-ZSM-5 structure along the [0 1 0] direction compressed in mwhich increase their occupancy upon compression (X3, X5, X8, X11, and X12); white(X1,X2, X4, X7, X9, and X10).

Figs. 2c, 4a and b and Table 2 show that the HP-induced struc-tural modifications of the cell parameters of Na-ZSM-5 compressedin m.e.w. are reversible upon pressure release down to ambientconditions.

3.3. HP-induced structural deformations of Na-ZSM-5 in m.e.w.

3.3.1. FrameworkThe HP-induced structural deformations were followed by 7

complete Rietveld structural refinements, performed from Pamb to1.6 GPa, and at Pamb (rev). Above 1.6 GPa, the quality of the data

.e.w. at Pamb, 0.3 GPa, 1.0 GPa, and Pamb (rev). Grey circles: extra-framework sitescircles: extra-framework sites which decrease their occupancy upon compression

Table 7Window openings (Å) of the straight and sinusoidal 10-ring channels of Na-ZSM-5 inthe pressure range Pamb �1.6 GPa.

Straight channelalong [0 1 0]

Sinusoidal channels along [1 0 0]

P (GPa) O5–O11 O1–O7 O15–O20 O24–O26 O23–O25 O17–O18

Pamb 5.46 5.76 5.59 5.50 5.63 5.710.1 5.39 5.51 5.38 5.32 5.67 5.340.3 5.45 5.67 5.35 5.38 5.75 5.270.8 4.69 6.11 5.45 5.53 5.40 5.361.0 4.86 6.02 5.38 5.35 5.21 5.281.6 4.30 6.35 5.35 5.34 5.29 5.30Pamb (rev) 5.51 5.80 5.56 5.65 5.64 5.59

Fig. 7. Pressure-dependence of the window ellipticity of the 10-ring straightchannel running along [0 1 0] upon compression in m.e.w.; the errors associatedwith these distances are smaller than the symbols used. The cross corresponds tothe value calculated for the structure reported to ambient conditions upon pressurerelease [Pamb (rev)].

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and the high number of structural parameters made it impossibleto obtain reliable structural data. The results of the refinementscorresponding to four selected pressure values (Pamb, 0.3 GPa,1.0 GPa, and Pamb (rev)) are reported in Tables 4–6 and shown inFigs. 5 and 6.

The structural variations induced in the framework up to1.6 GPa are minor, consistent with the small decrease of the unitcell parameters in this P-range (Da = 1.5%, Db = 0.7%, Dc = 0.8%,DV = 3.1%). Figs. 5 and 6 show that the 10-ring surrounding thechannel along [0 1 0] becomes more elliptic, while those surround-ing the channels along [1 0 0] become more circular and smaller.These observations can be quantitatively discussed on the basisof Table 7, which reports the dimensions of the window openingsin the straight channel (O5–O11 and O1–O7 distances; see Figs. 1aand 5) and in the sinusoidal channels (O15–O20, O24–O26, andO17–O18, O23–O25 distances; see Figs. 1b and 6) as a functionof pressure. Moreover, Fig. 7 reports the ellipticity of the straightchannel (defined as E[0 1 0] = (O1–O7)/(O5–O11) in [39]) vs. pres-sure: above 0.3 GPa the straight channel, which is rather circular atPamb, becomes much more elliptic. On the contrary, the shape ofthe sinusoidal channel openings tend to remain rather circularwith increasing P, while the aperture dimensions become signifi-cantly smaller than the original ones (Table 7).

3.3.2. Extra-framework sitesAt Pamb 12 extra-framework sites were located (labeled X1–X12

in Table 4), all with partial occupancies and, as a whole, corre-sponding to a content of 353 electrons. Most of these sites are atgreat distances from the framework oxygen atoms (Table 6), andhence it was impossible to assign them to either water moleculesor cations. Consequently, all the 12 sites were refined with the oxy-gen scattering curve. Table 6 shows that several X–X bond dis-tances are too short. Some of these are acceptable on the basis ofthe sum (lower than 1) of the occupancy factors of the sites in-volved, which are hence mutually exclusive. For others this sumis higher than 1, and hence it must be assumed that these sitesare actually occupied by both Na cations and water molecules.Due to the data quality and to the structure complexity, a more de-tailed description of the extraframework system is impossible.

Fig. 6. Projection of the Na-ZSM-5 structure along the [1 0 0] direction compressed in m.e.w. at Pamb, 0.3 GPa, 1.0 GPa, and Pamb (rev). Grey circles: extra-framework siteswhich increase their occupancy upon compression (X3, X5, X8, X11, and X12); white circles: extra-framework sites which decrease their occupancy upon compression(X1,X2, X4, X7, X9, and X10).

706 R. Arletti et al. / Microporous and Mesoporous Materials 142 (2011) 696–707

Table 4 shows that several extra-framework sites significantlyincrease their occupancy factor upon compression, due to the pen-etration of extra-molecules into these positions. This phenomenonis evidenced in Fig. 8a, which shows an increase of the total elec-tron number of the extra-framework sites as a function of pressure,in particular in the P-range 0.3–0.8 GPa. This is the same P-range inwhich the first discontinuity in the plot of the cell parameters vs.pressure is observed (Fig. 4). Fig. 8b and c show the change ofthe number of electrons of each extraframework site: the sitesX3, X5, X6, X8, X11, and X12 increase their occupancy, while theothers undergo an occupancy decrease. X1 is the only site whichempties upon compression (Fig. 8c).

As a whole, 89 additional electrons are found in the channels ofNa-ZSM-5 structure at 1.6 GPa, corresponding to an increase ofabout 25% with respect to the Pamb extra-framework content.Moreover, due to the impossibility of performing complete struc-ture refinements of the patterns collected at high P, it cannot be

Fig. 8. P-dependence of the electrons number of the extra-framework sites ofNa-ZSM-5 compressed in m.e.w. (a): total number (open symbols represent thenumber of extraframework electrons at Pamb after decompression); (b) and (c):number of electrons corresponding to selected extra-framework sites.

excluded that additional molecules penetrate the structure ofNa-ZSM-5 above 1.6 GPa and below 2.9 GPa. Above this latter pres-sure value, a strong increase of compressibility is observed(Fig. 4a), suggesting that the P-transmitting medium stops pene-trating the pores and that all pressure exerted on the sample actsdirectly for the compression of the structure. The P-induced in-crease of the extra-framework content observed in Na-ZSM-5 ismuch higher than the over-hydration observed in gismondine(5% [4]) and boggsite (19% [8]), the other two zeolites recentlystudied by our group. Also these two materials undergo aP-induced increase of the occupancy of already existing extra-framework sites without any cell volume expansion.

3.3.3. Reversibility of the HP-induced modifications in m.e.w.As can be seen in Figs. 2c and 4 and in Table 2, the reversibility

of the HP-induced phenomena in Na-ZSM-5 compressed in m.e.w.is complete as far as the unit cell parameters are concerned. On thecontrary, some structural deformations undergone by the frame-work and, above all, the positions of the extra-framework sitesare not completely restored upon P release (Figs. 5 and 6). Concern-ing the framework, the straight channel running along [0 1 0],which becomes more elliptic during compression (Figs. 5 and 7),almost perfectly regains its original shape upon decompression.

During compression, all the extra-framework sites undergo sig-nificant re-organization inside the cavities, as shown in Figs. 5 and6. This new distribution is not completely reversible because thepositions of the extra-framework sites present in Na-ZSM-5 at Pamb

are not exactly regained. This is particularly evident in the projec-tion along [1 0 0] (Fig. 6) and in Table 4, which shows that, i.e. theextraframework site X11 is no more present in the structure ofNa-ZSM-5 after P-release. The original extraframework electronnumber is also not completely recovered (Fig. 8a). This effect is alsoobserved in gismondine [4]; on the contrary, upon P release,boggsite [8] loses all the extra-molecules adsorbed duringcompression.

4. Concluding remarks

An investigation was conducted on the elastic behavior of Na-ZSM-5 in both s.o. and m.e.w., as ‘‘non-penetrating’’ and ‘‘penetrat-ing’’ pressure transmitting media, respectively. In both cases theunit cell parameters of Pamb are recovered upon decompression,but the effects of pressure on the crystallinity of the material aremuch higher in s.o. In this latter case the material is largely,

Fig. 9. Comparison of unit-cell volume variations as a function of pressure forNa-ZSM-5 compressed in silicone oil (squares) and (16:3:1) methanol:ethanol:water (circles). The lines represent the fits obtained using second-order Birch–Murnaghan equations of state. Black symbols correspond to the measurements indecompression.

R. Arletti et al. / Microporous and Mesoporous Materials 142 (2011) 696–707 707

although not completely, amorphized at the highest investigatedpressure, and the original pattern features are not recovered upondecompression (Fig. 2b and c).

Fig. 9 shows that Na-ZSM-5 compressibility is higher in s.o. thanin m.e.w. (K0 = 18.2(6) and 28.9(5) GPa, respectively). This result canbe interpreted as due to the penetration of extra- molecules, whichcontribute to contrasting P-induced channel deformation. In partic-ular, from the values of the refined linear axial bulk moduli of Na-ZSM-5 compressed in s.o. [K0(a) = 19.6(5); K0(b) = 20.4(3);K0(c) = 16.5(5)] and in m.e.w. [K0(a) = 21.2(5); K0(b) = 33.0(8);K0(c) = 33.1(10)], it is seen that the b and c axes become more rigidas a result of the mixed medium penetration. This can be interpretedfrom Figs. 5 and 6, which show the P-induced re-organization of theextra-framework sites of Na-ZSM-5 in m.e.w. In particular, greysites – which increase their occupancy upon compression (see alsoFig. 8b) – are mainly oriented along b and c. Moreover, some of thesesites are at short distances from other X sites (Table 6), so that a fur-ther decrease of b and/or c is hindered. Nevertheless, Na-ZSM-5 ishighly compressible when compared with the other zeolites studiedin m.e.w., and is the most compressible among those studied in‘‘non-penetrating’’ P-transmitting media [4,7,8].

It is worth noting that the extra-molecules penetration in Na-ZSM-5, although extremely high, occurs without any cell volumeexpansion, as in gismondine [4] and boggsite [8]. This can be ex-plained by the fact that no new extra-framework sites arise duringcompression and the only effect of the medium penetration is toincrease the occupancy factor of the numerous existing extra-framework sites. This phenomenon is only partially reversible,and hence a material with a different extraframework compositionis obtained at the end of the process.

Acknowledgements

The Swiss-Norwegian (BM01) beamline at ESRF is acknowl-edged for allocation of the experimental beamtime. The authorsare indebted to Simona Bigi and Gabriele Montagna for the chem-ical analysis of Na-ZSM-5. Two anonymous reviewers and theEditor Yvonne Traa greatly contributed with their comments toimprove the quality of the paper.

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