Elastic behavior of MFI-type zeolites: Compressibility of H-ZSM-5 in penetrating and non-penetrating media

The elastic behavior of H-ZSM-5 was investigated by in-situ synchrotron X-ray powder diffraction, using both silicone oil (s.o.) and (16:3:1) methanol:ethanol:water (m.e.w.) as “non-penetrating” and “penetrating” pressure transmitting media, respectively. From Pamb to 6.2 GPa the volume reduction observed in s.o. is 16.6%. This testifies that H-ZSM-5 is one of the most flexible microporous materials up to now compressed in s.o. Volume reduction observed in m.e.w. up to 7.6 GPa is 14.6%. A strong increase in the total electron number of the extraframework system, due to the penetration of water/alcohol molecules in the pores, is observed in m.e.w. This effect is the largest up to now observed in zeolites undergoing this phenomenon without cell volume expansion. The higher compressibility in s.o. than in m.e.w. can be ascribed to the penetration of the extra-water/alcohol molecules, which stiffen the structure and contrast the channel deformations.

High-pressure behavior of H-ZSM-5 compressed in (16:3:1) methanol:ethanol:water: (a) projection of the structure along the [0 1 0] direction at Pamb, 2 GPa and after pressure release to original ambient conditions (Pamb (rev)), and (b) P-dependence of the extraframework content expressed as total number of electrons (gray square represents the number of the extraframework electrons at Pamb after decompression).Figure optionsDownload as PowerPoint slideHighlights
► X-ray powder diffraction study of H-ZSM-5 compressibility.
► H-ZSM-5 is one of the softest porous material compressed in silicon oil.
► Penetration of additional water/alcohol molecules upon compression in m.e.w.
► Extra molecules contribute to stiffen the structure and to contrast HP effects.