Investigation of the Energetic Performance of Pure Silica ITQ-4 (IFR) Zeolite under High Pressure Water Intrusion Mohamed Ali Saada, † Se ´verinne Rigolet, † Jean-Louis Paillaud, † Nicolas Bats, ‡ Michel Soulard, † and Joe ¨l Patarin* ,† Equipe Mate ´riaux a ` Porosite ´ Contro ˆle ´e (MPC), Institut de Science des Mate ´riaux de Mulhouse (IS2M), LRC CNRS 7228, UniVersite ´ de Haute Alsace, ENSCMu, 3 Rue Alfred Werner, 68093 Mulhouse, France, and IFP-Lyon, Rond-Point de l’E ´ changeur de Solaize, B.P. 3, 69360 Solaize, France ReceiVed: March 24, 2010; ReVised Manuscript ReceiVed: May 27, 2010 To study the energetic performance of the 1D 12-membred-ring pure silica ITQ-4 zeolite (IFR topology), a high-pressure water intrusion-extrusion isotherm at room temperature was performed. The pressure-volume diagram indicates an irreversible phenomenon, water molecules remaining confined in ITQ-4 micropores. Therefore, the “water-ITQ-4” system appears to behave as a bumper. The water intrusion pressure and intruded volume are of 42 MPa and 0.136 mL/g, respectively. Investigations on the ITQ-4 samples by 29 Si and 1 H solid-state NMR spectroscopy and powder X-ray diffraction have confirmed the existence of a small amount of silanol defects in the nonintruded sample and an increase of these defects after the water intrusion-extrusion experiment. It appears clearly that one of the crystallographic silicon sites of the porous framework is particularly affected after such a treatment, leading to the creation of Si-OH groups by the breaking of siloxane bonds, these silanols being strongly hydrogen bonded with water molecules. 1. Introduction In the past decade, thermodynamics of confined systems involving water as nonwetting liquid and hydrophobic porous solid have attracted considerable attention due to their potential application in the field of energetics. 1,2 Gusev 3 and Eroshenko and Fadeev 4 have reported the discovery of this feature in the mid-1990s, following the investigation of heterogeneous systems made of water and silica gels. An extension to the functionalized organized mesoporous 5-7 and pure silica zeolites (zeosils) 1,8 was achieved later. Various zeosil materials, such as MFI, 1 *BEA, 2 DDR, 2 FER, 9 and CHA 10,11 were tested as water confining microporous matrices. Only some of them were considered as good candidates for energy storage. 11,12 Simultaneously to the experimental approach, great attention has been paid to the theoretical study of the water confined behavior by computer modeling 13-19 in order to get new insights into the various factors involved in the water intrusion-extrusion phenomenon. Zeosils are known as being hydrophobic materials. 20 To penetrate water in such microporous matrices, a certain pressure must be applied. 21 During this forced penetration (intrusion), the resulting mechanical energy can be converted into an interfacial one. Indeed, the massive 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 microporous zeosils. When the pressure is released, the system can evolve spontaneously by expelling water out of the cavities of the zeosil (extrusion) with a more or less significant hysteresis. 22 Consequently, the system allows accumulating and restoring significant amounts of energy. Diverse behaviors illustrated by pressure-volume diagrams can be observed depending on various physicochemical and topological parameters related to the porous framework such as hydrophobic/hydrophilic character, pore size and type (cages or channels), and channels dimensionality (1D, 2D, or 3D). According to phenomenon reversibility or irreversibility, the water-zeosils systems are able to restore, partly absorb, or completely dissipate mechanical energy. Consequently, molec- ular spring, shock-absorber, or bumper behaviors can be observed. 1,2,8,17 A water intrusion process has been applied to several zeosil materials with accessible pore opening. It was shown that the pure silica chabazite (Si-CHA) material having large cages with eight-membered ring (MR) openings acts as a molecular spring displaying a reversible water intrusion-extrusion isotherm with a pronounced hysteresis in the relax stage. 10 The purely siliceous DDR-type zeolite containing also 8-MR apertures presents an almost similar pressure-volume diagram. 2,23 The silicalite-1 (MFI topology), which is a 10-membered-ring pure silica zeolite, proved to behave as a molecular spring with an intrusion pressure around 100 MPa and an amount of stored energy about 10 J/(g of zeolite). 24 For the 12-membered-ring *BEA zeosil, which consists of at least 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 could explain its bumper behavior. 2 The purpose of this work is to assess the energetic perfor- mance, using a water intrusion-extrusion experiment, of the 1D microporous pure silica ITQ-4 material. This porous silica polymorph (IFR topology) is characterized by a large sinusoidal 12-MR channel (window size, 6.2 Å × 7.2 Å) parallel to the c-axis crystallographic direction in the monoclinic space group C2/m. 25-27 Thanks to its large void and pore aperture, such a topology appears to have potential applications in catalysis. Indeed, its Al-containing form was found to be an effective material for the hydroisomerization of short n-alkane chains and * To whom correspondence should be addressed. E-mail: joel.patarin@ uha.fr. † Universite ´ de Haute Alsace. ‡ IFP-Lyon. J. Phys. Chem. C 2010, 114, 11650–11658 11650 10.1021/jp102663f  2010 American Chemical Society Published on Web 06/10/2010