High-Pressure Water Intrusion Investigation of Pure Silica ITQ-7 Zeolite

Abstract

Experimental water intrusion–extrusion isotherms were recorded at room temperature on pure silica ISV-type zeolite (ITQ-7 zeosil) possessing a 3D channel system. The water intrusion is obtained by applying a high hydraulic pressure corresponding to the intrusion step. When the pressure is released, the water extrusion occurs but at a lower pressure to that of the intrusion one. The ITQ-7 zeosil–water system behaves like a shock-absorber, but the phenomenon is nonreproducible. Several characterizations have been realized before and after water intrusion–extrusion experiments in order to reveal the presence or the absence of defects after such experiments. Structural modifications at the long-range order can be observed by XRD analysis after intrusion. At the short-range order, solid-state NMR spectroscopy shows evidence of the presence of Q2 ((HO−)2Si(−OSi)2) and Q3 ((HO–Si(−OSi)3) or (Si(−OSi)3O–)) groups revealing the breaking of some siloxane bridges after the intrusion step. The amount of defects increases (<2% before and 15% after intrusion step). However, after a regeneration step (calcination of the intruded-extruded sample), the ITQ-7 zeosil–water system displays again a shock-absorber behavior with a similar intrusion pressure.