Investigation of the Energetic Performance of Pure Silica ITQ-4 (IFR) Zeolite under High Pressure Water Intrusion

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 29Si and 1H 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.