Energetic Performances of Channel and Cage-Type Zeosils

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Energetic Performances of Channel and Cage-Type Zeosils Lydie Tzanis-Daou, Mickaël Trzpit, Michel Soulard, and Joël Patarin J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/jp305632m • Publication Date (Web): 04 Sep 2012 Downloaded from http://pubs.acs.org on September 11, 2012

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The Journal of Physical Chemistry

Energetic performances of channel and cage-type zeosils Lydie Tzanis, Mickaël Trzpit, Michel Soulard, Joël Patarin* Université de Haute-Alsace (UHA), CNRS, Equipe Matériaux à Porosité Contrôlée (MPC), Institut de Sciences des Matériaux de Mulhouse (IS2M), LRC 7228, F-68093 Mulhouse *Corresponding author: E-mail: [email protected] Tel: ++33 (0)3 89 33 68 80; Fax: ++33 (0)3 89 33 68 85

ABSTRACT Energetic performances of nine channel or cage-type zeosils (AFI, FER, MFI, MEL, TON, MTW, DDR, STT and CHA-type pure silica zeolites) are obtained using water intrusionextrusion isotherms. The water intrusion is obtained by applying a high hydraulic pressure corresponding to the intrusion step. When the pressure is released, these nine “zeosil-water” systems behave like a molecular spring; water being spontaneously expelled out of the cavities of the zeosils (extrusion step). The first part of this study details the energetic characteristics of MEL-type zeosil (Silicalite-2) which displays a molecular spring behavior reproducible over several water intrusion-extrusion cycles. However, solid state NMR spectroscopy revealed the presence of structure defects (>5%) which are responsible for the low value of the stored energy (6.5 J/g of zeosil). In a second part, the energetic properties of the nine channel or cage-type zeosils are compared. For these samples, structural modifications can be observed by solid state NMR spectroscopy. An overall view of the characteristics derived from the water intrusion-extrusion isotherms of these nine zeosils are discussed. The relation between the structure type in particular the porous system (cages or channels) and the intrusion pressure is studied to better understand the mechanism of water intrusion and to predict the zeolite behavior (intrusion pressure values) for a given structure type. The Laplace-Washburn relationship seems to be not appropriate for microporous ACS Paragon Plus Environment


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materials. A correlation was found between the intrusion pressure and the pore diameter for channel systems and the largest cage size for cage systems.

KEYWORDS: hydrophobic zeolites, energetic behavior, intrusion pressure, MEL-structure type.

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1. Introduction

Microporous materials are used in several industrial processes such as petrochemistry, catalysis, adsorption and separation, due to their characteristics such as low density, large free volume, void spaces in the form of channels and cages, acid/base properties and thermal stability [1]. Another application for zeolites is in energetic: transforming mechanical energy into interfacial energy. The principle of this application is based on thermodynamic systems, between a liquid and a lyophobic porous matrix [2]. By submitting these systems to an increasing hydrostatic pressure, the intrusion of the liquid into the pores of the solid is observed when the pressure P becomes equal to the capillary pressure Pc which can be expressed by the Laplace-Washburn relation: [3] Pc = - 4γLcos θ / D

eq 1

Where γL is the interface energy (or surface tension), D the pore diameter and θ the contact angle between the liquid and the solid surface (θ > 90°). During the intrusion of a non wetting liquid into a microporous material, a large interface Ω carrying the surface free energy is produced. The development of this surface (∆Ω > 0), leads to an increase in the Gibbs energy (∆G > 0) which can be given by the following relation: ∆G = - γL cos θ ∆Ω

eq 2

When the pressure is released, to minimize this energy (∆G < 0), the system spontaneously reacts and decreases its solid/liquid interface (∆Ω < 0) by extrusion of the liquid out of the cavities of the solid [4]. This mechanical energy corresponds to a work (W), more exactly to a displacement force which can be expressed as: Vf

W=

∫

− PdV

eq 3

V0

Where P is the pressure, V0 is the initial volume and Vf is the final volume. It is in the eighties that Eroshenko proposed to use these properties in the energetic field and more exactly to adsorb, store or dissipate energy [5-7]. Recently, the choice of this ACS Paragon Plus Environment


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heterogeneous system focuses on the water intrusion into hydrophobic porous materials [8-10]. For microporous solids, this type of application is mainly opened to pure silica zeolites (zeosils) which are well known for their hydrophobic character. During the forced intrusion, the bulk water is transformed into a multitude of molecular clusters developing a large zeosil-water interface. From a microscopic point of view, this fact can be explained by the breaking of intermolecular bonds in the water to create new bonds with the silica framework of the microporous zeosil. Depending on the “zeosil-water” system, when the pressure is released (extrusion), the system is able to restore, dissipate or absorb the supplied mechanical energy during the compression step with a more or less significant hysteresis and therefore to display a spring, shock-absorber or bumper behavior. Several results with “zeosil-water” systems have been already obtained. Thus, the pure silica chabazite (CHA), a cage-like structure with 8-membered ring (MR) openings, acts as a molecular spring displaying a reversible water intrusion-extrusion isotherms with a pronounced hysteresis in the relax stage [11, 12]. The purely siliceous STT and DDR-type zeolites containing 7, 9 and 8 MR apertures, respectively, present an almost similar pressure-volume diagram [13, 14]. For the 12membered ring *BEA-type zeosil which consists at least in two polytypes, the water intrusion process is irreversible and no energy can be restored. The presence of defect sites at the interface of the two polytypes was advanced to explain the bumper behavior [14]. More recently, it was shown that the FER [15] and RRO [16]-type zeosils display a spring and shock-absorber behavior, respectively. The most studied solid was the MFI-type zeosil (Silicalite-1); a pure silica zeolite with a three-dimensional 10 MR channel system which acts as a molecular spring with an intrusion pressure around 100 MPa [17] and a stored energy of about 10 Joules per gram of zeolite. On this last zeosil, molecular modelling [18, 19] and calorimetric measurements [20] get evidenced on the presence of defect sites (silanol groups) and their influence on the characteristics of the water intrusion-extrusion isotherms and the stored energy. The energetic performance, of zeosils characterized by a 1D channel system with 12 or 10 MR such as AFI, MTW and TON- type zeosils has been also studied [21]. ACS Paragon Plus Environment

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In the first part of this study, the energetic performance of Silicalite-2 (MEL-structure type), using water intrusion-extrusion experiments are presented. This sample was fully characterized before and/or after water intrusion mainly by powder X-ray diffraction, SEM, thermal analysis, N2 adsorption-desorption and

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Si NMR spectroscopy. The stored energy

was evaluated from the pressure-volume diagrams of the “zeosil-water” system. In the second part, the energetic behavior of nine zeosils presenting a spring molecular behavior were compared: three 1-D channel zeosils (AFI, MTW and TON-structure type) three multichannel zeosils (MFI, FER and MEL-structure type) and three cage-like structures (STT, DDR and CHA-type zeosils). A correlation was found between the intrusion pressure and the pore diameter for channel systems and the largest cage size for cage systems.

2. Experimental section 2.1. Synthesis of pure silica MEL-type zeolites Among these several zeosils presented through this work, only the Silicalite-2 (MELstructure type) has not been evaluated for their energetic performances, so its synthesis and characterization will be described here. The MEL-type zeosil (Silicalite-2) was synthesized according to the procedure published by Nakagawa [22]. Aerosil 130 (SiO2, Degussa) was mixed with 3,5-dimethyl-N,Ndiethylpiperidinium hydroxide (DMDEPOH) in distilled water. The suspension was stirred for 1h at room temperature, then in an ultrasonic bath during 1 h to improve homogeneity. After aging for 12 h, the mixture was transferred to a 120 mL Teflon-lined stainless steel autoclave and heated for 50 days at 170°C. The as-made sample was then calcined during 5 hours at 600 °C under air to completely remove the organic template. Concerning the other zeosils the composition of the starting mixture is summarized in Table 1. ACS Paragon Plus Environment


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2.2. Characterization X-ray diffraction patterns of the different samples were recorded in a Debye-Scherrer geometry, on STOE STADI-P diffractometer equipped with a curved germanium (111), primary monochromator and a linear position sensitive detector (6 °2θ) using Cu Kα1 radiation (λ = 0.15406 nm). Measurements were achieved for 2θ angle values in the 5–50 range, step 0.06 °2θ and time/step = 900 s. The unit-cell parameters were determined using Louër’s DICVOL91 indexing routine [23] of the STOE WinXPOW program package [24]. The size and the morphology of the crystals were determined by scanning electron microscopy (SEM) using a Philips XL 30 FEG microscope. Thermogravimetric (TG) and differential scanning calorimetry (DSC) analyses were carried out on a Setaram Sensys Evo TG-DSC apparatus, under nitrogen–argon flow, with a heating rate of 5 °C min-1 from 20 to 700 °C. Prior to the analysis, the samples were hydrated in a 80% relative humidity atmosphere during 24h in order to set the hydration state. Nitrogen adsorption isotherms were performed using a Micromeritics ASAP 2420 apparatus. Prior to the adsorption measurements, the calcined samples were outgassed at 350 °C overnight under vacuum. The specific surface area (SBET) and microporous volume (Vmicro) were calculated using the BET and t-plot methods, respectively. 29

Si MAS and 1H–29Si CPMAS NMR spectra were recorded on a Bruker Advance II

300 MHz spectrometer. The recording conditions are given in Table 2. The intrusion–extrusion of water in the zeosil samples were performed at room temperature using a modified mercury porosimeter (Micromeritics Model Autopore IV) as described in our previous works [11]. The experimental intrusion-extrusion curves were obtained after subtraction of the curve corresponding to the compressibility of pure water. The values of the intrusion (Pi) and extrusion (Pe) pressures correspond to that of the half volume total variation. Pressure is expressed in MPa, and volume variation in mL per gram of


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anhydrous calcined samples. The experimental error is estimated to 1% on the pressure and on the volume.

3. Results and discussion 3.1. XRD and SEM characterizations

After synthesis, the purity of the calcined MEL-type zeosil was checked by XRD analysis. The XRD patterns of the calcined samples before and after water intrusion-extrusion experiments are reported in Figure 1. According to Piccione et al. [25], the sharpness of the XRD peaks attests the absence of MEL/MFI intergrowths and the presence of the two peaks (110) and (330), marked with an asterisk (Figure 1a), confirm the obtention of pure Silicalite-2 zeosil. No significant changes are observed between the powder X-ray diffractograms of the calcined Silicalite-2 samples (before and after water intrusion-extrusion experiments) which mean that no modifications occur at the long-range order. They are indexed with the following unit-cell parameters: a= 20.030(3) Å, c= 13.389(2) Å and after intrusion: a= 20.031(2) Å, c= 13.390(2) Å (tetragonal symmetry, I-4m2 space group). The crystal morphology of Silicalite-2 was examined by scanning electron microscopy. The micrograph is given in Figure 2. The Silicalite-2 zeosil displays a rectangular parallelepiped shape. The size is 1 x 1 µm2 with a length ranging from 2 to 5 µm. 3.2. N2 Adsorption-desorption isotherms. The N2 adsorption-desorption isotherms of the calcined sample are shown in Figure 3. These isotherms are mainly of type I characteristic of microporous solids. The BET surface area and micropore volume are 440 m².g-1 and 0.18 cm3.g-1, respectively. 3.3. Thermal analysis. The thermogravimetric curves of this zeosil before and after intrusion of water are reported in Figure 4. Two steps are observed. The first loss, between 20 and 200 °C, is ACS Paragon Plus Environment


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ascribed to the desorption of physisorbed water molecules (1.7 wt% before and 1.9 wt% after intrusion–extrusion of water). The second step, in the temperature range 250-650 °C could arise from dehydroxylation reactions. For the non-intruded sample the total weight loss is quite low 2.6 wt%. After water intrusion-extrusion experiments no significant changes are observed, with a total weight loss of 2.8 wt%. These weight losses correspond to nearly 8 and 9 water molecules per unit cell (96 SiO2), respectively.

3.4 29Si MAS and 1H–29Si CPMAS NMR spectroscopy. 29

Si MAS NMR spectroscopy

The

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Si MAS NMR spectra of the calcined MEL-type zeosil before and after water

intrusion-extrusion experiments are shown in Figure 5. The spectra of the non intruded and intruded samples are quite similar and exhibits three main signals located between -108 and 120 ppm associated to Q4 groups (Si-(OSi)4) and corresponding to the 7 non-equivalent crystallographic sites of the structure (Figure 5). In both cases, a broad component at about 102 ppm is also observed. The latter is characteristic of Q3 sites and reveals the presence of silanol (Si-(OSi)3OH) or (Si-(OSi)3O-) groups. The existence of Q3 sites before (5% of total Si) and after water intrusion (5.3 % of total Si) is in good agreement with the thermogravimetric results. From these NMR spectra, it appears that structure defects are present in both samples. 1

H–29Si CPMAS NMR spectroscopy

The 1H–29Si CPMAS NMR spectra of the calcined non-intruded and intruded samples are reported in Figure 6. These spectra were performed in order to enhance the silicon atoms that bear protons and thus to get evidence of the presence of silanol groups. The 1H–29Si CPMAS technique does not provide quantitative results, however, it allows a relative comparison of the spectra if they were registered under the same conditions. The different spectra show the presence of a resonance at around -92 ppm corresponding to Q2 sites. This signal is more pronounced after intrusion-extrusion experiments. According to the signal to ACS Paragon Plus Environment

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noise ratio, after water intrusion-extrusion experiments, the Q3 and Q2 components increase. Such a result indicates that during the forced intrusion of water, the breaking of some siloxane bonds occurs.

3.5 Water intrusion-extrusion: pressure–volume diagrams

The pressure–volume diagrams of the MEL-type zeosil (Silicalite-2 sample) after one and three water intrusion-extrusion cycles are given in Figure 7 and the characteristic data in Table 3. The intrusion-extrusion of water is reproducible over several cycles. For the MEL-type zeosil, the intrusion curves are completely superimposable and a same behavior is observed for the extrusion curves. However an important spread of the intrusion step is observed. The intrusion of water starts at around 20 MPa with a complete filling of the pores around 150 MPa. The large spreading of the intrusion step could be explained by the presence of Q3 and Q2 sites in the calcined material as revealed by

29

Si MAS and 1H–29Si CPMAS

NMR. The intruded volume is around 0.105 mL.g-1 and the average value for the intrusion pressure is reached at Pi = 63 MPa. At the relaxation, the extrusion pressure is slightly lower (Pe = 58 MPa). It should be noted that this volume is slightly lower than the one determined from N2 desorption measurements (i.e., 0.18 mL/g). As shown by Debiens et al. [18] for Silicalite-1 and Trzpit et al. [12] for CHA-type zeosil, the value of the intruded volume determined for a water density of 1 has to be corrected since the average computed water density in the MFI and CHA structures is around 0.6 g/mL. In this case too, the density of bulk water is lower than 1 and close to 0.6. This “zeosil-water” system shows a spring behavior with a stored energy close to 6.5 J per gram of zeosil. Compared to the defect-free silicalite-1 [17] where the stored energy is equal to 10 J/g and despite a similar pore opening in both zeosils (5.3-5.4 Å and 5.1-5.6 Å for MEL and MFI, respectively), the energy loss reaches about 40 %. ACS Paragon Plus Environment


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3.6 Relationship between the intrusion pressure and the pore openings of zeosils The aim of this part is to correlate the intrusion pressure values with several parameters of the zeolitic structures such as the pore system (channels or cages), its dimensionality (mono or multichannels), the pore or cage sizes,... in order to predict the energetic behavior of other zeolitic structures. These characteristics are reported in Table 3. As it can be seen, the intrusion pressures for the 1D channel AFI, MTW and TON-type zeosils, are around 60, 130, and 190 MPa for pore diameters of 7.3 Å, 5.6-6.0 Å and 4.6-5.7 Å, respectively. As expected when the channel diameter decreases the intrusion pressure increases. Similar conclusions can be done for the multichannels MFI and FER structures. The relative intrusion pressures are equal to 100 and 150 MPa for pore diameters ranging from 5.1-5.6 Å and 3.5-5.4 Å, respectively. The MEL-type does not follow this trend; the intrusion pressure being close to 60 MPa for pore openings between 5.3 to 5.4 Å. However, the studied sample shows a larger amount of defects (see NMR results) compared to the other multichannel structures. Overall, the zeosils studied are able to restore around 90% of the stored energy. The FER, MFI, MTW and TON-type zeosils can store the largest amount of energy (between 10.6 to 15.0 J/g of zeosil). The lower energy storage of AFI, and MEL-types seems to be due to the incommensurate structural modulation along the C-axis (presence of few stacking defects along the channel axis) [21], and the presence of structure defects before the intrusion step, respectively.

The second group concerns the cage-like structures (CHA, STT and DDR-type zeosils), where the energy stored is around 6 J per gram of zeosil. The intrusion pressures are equal to 37, 40 and 60 MPa for window diameters of 3.8 Å, 2.4-5.3 Å and 3.6-4.4 Å for CHA, STT, and DDR-type zeosils, respectively. Surprisingly, these intrusion pressures are lower than those of channel systems, whereas the window openings are smaller. This would mean that ACS Paragon Plus Environment

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the intrusion pressure would be better related to the diffusion of water in the structure than to the pore openings.

3.7 Validity of the Laplace-Washburn relation The Laplace-Wahsburn relation (equation 1) is not appropriate to describe the intrusion of water in microporous solids [26]. However, it was interesting to check the nonvalidity of this law for this kind of materials. It has been applied on the different zeosils where two parameters were highlighted: a) the intrusion pressure and the pore diameter for channel systems, b) the intrusion pressure and the pore (window) diameter or the cage size for cagelike systems. The results are shown in Figure 8. According to the equation (1) and considering in a first approximation that, the surface tension γ and the contact angle θ do not vary with the pore diameter which in not really true, the intrusion pressure should be proportional to the inverse of the pore diameter. For zeosils characterized by 1D and 3D channel systems, it seems possible to align more or less the dots on two different lines (one for 1D and one for 3D) with a similar slope (see Figure 8). The fact that all the points for 1D and 3D zeosils cannot be aligned on one line confirms that the surface tension γ and the contact angle θ depend also on the dimensionality of the channel system. For cage-like zeosils, no relationship can be found between the intrusion pressure and the inverse of the average window diameter (see black triangles in figure 8). However, taking into account the largest cage size (calculated from the structure data [27] and using the Diamond program [28-29]), the dots can be aligned on one line (see empty triangles in figure 8). For all zeosils (except for the MEL-type: too much silanol defects), the intrusion pressure was plotted versus the largest cage size for cage systems and the pore diameter for channel systems (figure 9). The tendency was fitted with the following polynomial (eq 4): P= A0+ A1x1 + A2x2 + A3x3 , with x = 1/D

eq 4

Where P is the intrusion pressure (MPa), D the pore diameter or the largest cage size (Å) and An, (n = 0 to 3) four constants. ACS Paragon Plus Environment


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The calculated trend curve (A0= -0.42, A1=650, A2= -159, and A3= 14) correlates with the experimental data with a coefficient R² close to 0.81. The presence of defect sites, the dimensionality of the channel system or the shape of the cages can explain the quite low value of this coefficient.

4. Conclusions The energetic performances of nine channel or cage-type zeosils (AFI, FER, MFI, MEL, TON, MTW, DDR, STT and CHA-type pure silica zeolites) determined from water intrusion-extrusion isotherms were compared. All these “zeosil-water” systems display a molecular spring behavior reproducible over several cycles and therefore they are able to store and restore energy. It is the case for instance of the MEL-type zeosil (Silicalite-2 sample). However, in that case the intrusion pressure and consequently the stored energy are quite low. The presence of structure defects evidenced by solid-state NMR can explain such a result. As expected, for the channel-type zeosils, the water intrusion pressure is related to the pore opening of channels; the intrusion pressure increases when the pore diameter decreases. On the contrary, for the cage-like zeosils, no direct relationship was found between the intrusion pressure and the pore openings. Indeed, the intrusion pressures are lower than those observed for channels systems, while the pore openings are smaller. Consequently, the stored energy is the highest for zeosils characterized by a porous channel system. In the case of the cage-like systems, it is the cage size which influences the intrusion pressure and not the size of window openings. A correlation was found between the intrusion pressure and the pore diameter for channel systems and the largest cage size for cage systems. These results confirm that the intrusion pressure and the ability to store and restore the energy depend on various physical parameters related to the porous material such as the pore system (cavities or channels), the pore size, the dimensionality of the channel system and the presence or not of structure defects.


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Acknowledgment This work was supported by the French Agence Nationale de la Recherche through the ANR program “Heter-eau”, under Contract No. BLAN 06-3_144027. The authors also thank Dr. S. Rigolet and Dr. T.J. Daou for fruitful discussions.

References [1] Cejka, J.; Van Bekkum, H.; Corma, A.; Schüth, F. Introduction to Zeolite Science and Practice. Studies in Surface Science and Catalysis 168,3rd revised ed.; Elsevier B.V.: Amsterdam, The Netherlands, 2007; p 525. [2] Eroshenko, V.; Entropie, 1997, 202/203, 110-117. [3] Washburn, E.W.; Phys. Rev. 1921, 17, 374-375. [4] Eroshenko, V.; Int. Pat. WO 96/18040, 1996. [5] Eroshenko, V.; C.R. Acad. Sci. Ukraine, Série A, 1990, 10, 79-81. [6] Eroshenko, V.; Brevet SU1333870, 1982. [7] Eroshenko, V.; Brevet SU943444, 1987. [8] Eroshenko, V.; Regis, R.C.; Soulard, M.; Patarin, J.; J. Am. Chem. Soc. 2001, 123, 81298130. [9] Martin, T.; Lefevre, B.; Brunel, D.; Galarneau, A.; Di Renzo, F.; Fajula, F.; Gobin, P.F.; Quinson, J.F.; Vigier, G.J.; Chem. Comm. 2002, 1, 24-25. [10] Fadeev, A.Y.; Eroshenko, V.; J. Colloid and Interface Sci. 1997, 187, 275-282. [11] Trzpit, M.; Soulard, M.; Patarin, J.; Chem. Lett. 2007, 36, 980-981. [12] Trzpit, M.; Rigolet, S.; Paillaud, J.-L.; Marichal, C.; Soulard, M.; Patarin, J.; J. Phys. Chem. B, 2008, 112, 7257-7266. [13] Tzanis, L.; Trzpit, M.; Soulard, M.; Patarin, J.; J. Phys. Chem. C, 2012, 116, 4802-4808. [14] Soulard, M.; Patarin, J.; Eroshenko, V.; Regis, R.C.; In Recent Advances in the Science and Technology of Zeolites and Related Materials, in: E. Van Steen, L. Callanan, M. Claeys



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(Eds.), Proceedings of the 14th International Zeolite Conference, Studies in Surface Science and Catalysis 154 (2004) pp. 1830. [15] Cailliez, F.; Trzpit, M.; Soulard, M.; Demachy, I.; Boutin, A.; Patarin, J.; Fuchs, A. H.; Phys. Chem. Chem. Phys., 2008, 10, 4817-4826. [16] Saada, M.-A.; Soulard, M.; Marler, B.; Gies, H.; Patarin, J.; J. Phys. Chem. C, 2011, 115, 425-430. [17] Eroshenko, V.; Regis, R.C.; Soulard, M.; Patarin, J.; C. R. Phys. 2002, 3, 111-119. [18] Desbiens, N.; Demachy, I.; Fuchs, A. H.; Kirsh-Rodeschini, H.; Soulard, M.; Patarin, J.; Angew. Chem. Int. Ed. 2005, 44 5310-5313. [19] Trzpit, M.; Soulard, M.; Patarin, J.; Desbiens, N.; Cailliez, F.; Boutin, A.; Demachy, I.; Fuchs, A.; Langmuir, 2007, 23, 10131-10139. [20] Karbowiak, T.; Saada , M.–A.; Rigolet, S.; Ballandras, A.; Weber, G.; Bezverkhy, I.; Soulard, M.; Patarin, J.; Bellat, J.-P.; Phys. Chem. Chem. Phys. 2010, 12, 11454-11466. [21] Tzanis, L.; Trzpit, M.; Soulard, M.; Patarin, J.; Micropor. Mesopor. Mater. 2011, 146, 119-126. [22] Nakagawa, Y.; Brevet WO 95/09812, 1995. [23] Boultif, A.; Louër, D.; J. Appl. Crystallogr. 1991, 24, 987-993. [24] STOE WinXPOW ; version 1.06 ; STOE and Cie GmbH : Darmstadt, Germany, 1999. [25] Piccione, P.M.; Davis, M.E.; Micropor. Mesopor. Mater. 2001, 49, 163-169. [26] Lefevre, B. ; Saugey, A. ; Barrat, J.L ; Bocquet, L. ; Charlaix, E. ; Gobin, P.F. ; Vigier, G. ; J. Chem. Phys., 2004, 120, 4927-4938. [27] Baerlocher, C.; McCusker, L.B.; Olson, D.H.; Atlas of Zeolite Framework Types, Sixth revised edition, Elsevier B.V., Amsterdam, 2007, also available on the web at www.izastructure.org/databases/. [28] Penningtona, W.T.; J. Applied Crystallography, 1999, 32, 1028-1029. [29] Diamond, version 3.1, CRYSTAL IMPACT GbR, Bonn, Germany, 1997.


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Table 1 Synthesis conditions of the different zeosils (molar composition, structure-directing agent (SDA), temperature (T) and time (t)). Sample StructureT t Molar composition Ref. (Structure directing agent (°C) (days) type) (SDA) SSZ-24 1SiO2: 0.14 SDA : 0.1 KOH : 32 H2O TMAdaOH(a) 150 15 21 (AFI) ZSM-12 M4BQ(OH)2(b) 175 12 21 1 SiO2: 0.25 SDA : 0.5 HF: 50 H2O (MTW) ZSM-22 1-butylamine 150 12 21 1 SiO2: 1.0 SDA : 1 HF : 20 H2O (TON) Chabazite 1 SiO2: 0.5 SDA : 0.5 HF : 3 H2O TMAdaOH 150 4 11 (CHA) Decado1-Adamantadecasil 3R 1 SiO2: 0.4 SDA : 4 EN(c) : 60 H2O 180 20 14 namine (DDR) SSZ-23 1 SiO2: 0.5 SDA : 0.5 HF : 15 H2O TMAdaOH 150 30 13 (STT) Ferrierite 1.5 SiO2:2 HF-SDA:4 PrNH2 :16 SDA:8 H2O Pyridine 180 5 15 (FER) Silicalite-1 1 SiO2: 0.1 SDA : 0.2 NH4F : 30 H2O TPABr(d) 200 7 17 (MFI) Silicalite-2 This 1 SiO2: 0.1 SDA : 5 H2O DMDEPOH(e) 170 50 (MEL) work (a) N,N,N-trimethyladamantammonium, (b) Tetramethylene bisquinuclidinium diquaternaire dihydroxide, (c) Ethylenediamine, (d) Tetrapropylammonium bromide, (e) 3,5-dimethyl-N,Ndiethylpiperidinium hydroxide.



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Table 2 Recording conditions of the 29Si MAS and 1H-29Si CPMAS NMR spectra of the MELtype zeosil 29 29

Si MAS Si

Chemical shift standard Frequency (MHz) 59.6 Pulse width (µs) 2.0 Flip angle π/6 Contact time (ms) / Recycle time (s) 80 Spinning rate (kHz) Scans number 1360 a TMS : TetraMethylSilane b The relaxation time t1 was optimized

1

H-29Si CP MAS 29 H Si a TMS 300.14 59.6 4.1 4.1 π/2 / 1 7b 7 4 8 12000 1


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Table 3 Characteristics of the samples, intrusion (Pi) and extrusion (Pe) pressures, intruded volume (Vi), stored (Es) and restored (Er) energies. Dimension Intruded Es = Er= Sample Ring Pore Energy Pi ality of the Pe volume Stored Restored (Structure Size opening yield energy energy channel (MPa)a (MPa)a Vi type) (T)* (Å) (%)c a b b system (mL/g) (J/g) (J/g) SSZ-24 (AFI) 12 1D 7.3 58 55 0.102 5.8 5.6 97 ZSM-12 (MTW)

12

1D

5.6-6.0

132

126

0.114

15.0

14.4

96

ZSM-22 (TON)

10

1D

4.6-5.7

186

172

0.075

14.0

12.7

92

Chabazite (CHA)

8

Cages

3.8

37

31

0.148

5.5

4.6

84

DD3R (DDR)

8

Cages

3.6-4.4

60

51

0.112

6.7

5.7

85

SSZ-23 (STT)

7 9

Cages

2.4-3.5 3.7-5.3

40

33

0.135

7.0

5.6

80

Ferrierite (FER) Silicalite-1 (MFI)

8 10

2D

3.5-4.8 4.2-5.4

147

142

0.102

15.0

14.5

97

10

3D

5.1-5.6

96

91

0.110

10.6

10

94

Silicalite-2 10 3D 5.3-5.4 63 58 0.103 6.5 5.9 91 (MEL) * T : number of silicon (a) Determined from the water intrusion-extrusion isotherms (b) The stored (Es) or restored (Er) energy, corresponding to the area located between the relevant Vf

curve of intrusion or extrusion, respectively and the volume axis (Fig. 7), is given by: E = ∫ PdV , V0

where V0 is the initial volume and Vf is the final volume. (c) % Energy yield = Es x100 Er



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a

*

*

b

5

10

15

20

25 30 2θ° (CuΚα1)

35

40

45

50

Figure 1. X-ray diffraction patterns of calcined Silicalite-2 samples before (a) and after water intrusion-extrusion experiments (b). The sharpness of the peaks indicates the absence of the MEL/MFI intergrowths.* (110) and (330) peaks of the MEL structure.

18 Environment ACS Paragon Plus

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Figure 2. SEM micrograph of calcined Silicalite-2 sample.



140 120 100

3

Adsorbed Volume (cm /g) STP

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80 60

Adsorption Desorption

40 20 0 0.0

0.2

0.4

0.6

0.8

1.0

Relative Pressure P/P0 Figure 3. N2 adsorption-desorption isotherms of calcined Silicalite-2 sample at 77 K.


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0.0

-0.5

Weight Variation (%)

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-1.0

-1.5

-2.0

-2.5

-3.0 0

100

200

300

400

500

600

Temperature (°C) Figure 4. TG curves of calcined Silicalite-2 sample before (solid line) and after water intrusion-extrusion experiments (dotted line).


700


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Q4

Q3

-80

-90

-100

-110

-120

-130

δppm/TMS Figure 5. 29Si MAS NMR spectra of calcined Silicalite-2 sample before (thick solid line) and after water intrusion-extrusion experiments (fine line).


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Q3

Q2

-80

Q4

-90

-100

-110

δppm/TMS

-120

Figure 6. 1H-29Si CPMAS NMR spectra of calcined Silicalite-2 sample before (thick solid line) and after water intrusion-extrusion experiments (fine line).


-130


0.12

0.10

Volume Variation (mL/g)

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0.08

0.06

Intrusion cycle 1 Extrusion cycle 1 Intrusion cycle 2 Extrusion cycle 2 Intrusion cycle 3 Extrusion cycle 3

0.04

0.02

0.00 0

30

60

90

120

150

180

Pressure (MPa) Figure 7. Pressure-volume diagrams of the “Silicalite-2-water” system.


210

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200

Average diameter of pore openings for 1D channel zeosils

TON

180 Intrusion Pressure ( MPa)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Average diameter of pore openings for multichannels zeosils

160 FER

140

Average diameter of pore (window) openings for cage-like zeosils

MTW

120

Largest cage size for cage-like zeosils

MFI

100 80

AFI

DDR

60 STT

40

CHA

1D channel zeosils Multichannels zeosils Cage-like zeosils

MEL DDR CHA

STT

20 0 0.00

0.05

0.10

0.15

0.20

1 / Diameter

0.25

(Å-1)

0.30

0.35

0.40

Figure 8. Graph of the intrusion pressure (MPa) versus the inverse of the average diameter of the pore openings for channel systems and the largest cage size for cage-like structures.



200

Average diameter of pore openings for 1D channel zeosils Average diameter of pore openings for multichannels zeosils Largest cage size for cage-like zeosils

TON

180 160

Intrusion pressure (MPa)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

FER MTW

140

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Trend curve

120 100

MFI 80

DDR

60

STT

AFI

40

CHA

20 0 3

4

5

6

7

8

9

10

11

12

13

Diameter (Å) Figure 9. Graph of the intrusion pressure (MPa) versus the average diameter of the pore openings for channel systems and the largest cage size for cage-like structures.


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Energetic Performances of Channel and Cage-Type Zeosils

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