Strain of MFI crystals in membranes: An in situ synchrotron X-ray study

Temperature-resolved in situ synchrotron X-ray diffraction is used for the first time to study the microstructure evolution of a preferentially oriented zeolite membrane (siliceous ZSM-5) during calcination of the organic structure directing agent (tetrapropyl ammonium, TPA). Use of transmission sample geometry allowed us to discriminate in-plane from out-of-plane reflections and to calculate strain imposed on the zeolite layer along the in-plane (parallel to the support) as well as the out-of-plane (perpendicular to the support) direction over the entire calcination process. The results strongly suggest that the zeolite crystals of the membrane are under compressive in-plane stress and that their thermal behavior is quite different from free standing powder.