ZSM-5 decrystallization and dealumination in hot liquid water

Physical Chemistry Chemical Physics : PCCP
Alex R MaagMichael T Timko

Abstract

Zeolites have recently attracted attention for upgrading renewable resources in the presence of liquid water phases; however, the stability of zeolites in the presence of liquid-phase water is not completely understood. Accordingly, the stability of the ZSM-5 framework and its acid sites was studied in the presence of water at temperatures ranging from 250 to 450 °C and at pressures sufficient to maintain a liquid or liquid-like state (25 MPa). Treated samples were analyzed for framework degradation and Al content and coordination using a variety of complementary techniques, including X-ray diffraction, electron microscopy, N2 sorption, 27Al and 29Si NMR spectroscopy, and several different types of infrared spectroscopy. These analyses indicate that the ZSM-5 framework retains >80% crystallinity at all conditions, and that 300-400 °C are the most aggressive. Decrystallization appears to initiate primarily at crystal surfaces and share many characteristics in common with alkali promoted desilication. Liquid water treatment promotes ZSM-5 dealumination, following a mechanism analogous to that observed under steaming conditions: initiation by Al-O hydrolysis, Al migration to the surface, and finally deposition as extra framework A...Continue Reading

References

Apr 14, 2007·Langmuir : the ACS Journal of Surfaces and Colloids·Ryan L Hartman, H Scott Fogler
Feb 28, 2015·Chemistry : a European Journal·Daniel FodorJeroen A van Bokhoven
Aug 25, 2015·Journal of the American Chemical Society·Lu ZhangDaniel E Resasco
Nov 29, 2016·Nature Nanotechnology·Kumar Varoon AgrawalMichael S Strano

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Citations

Aug 12, 2020·Advanced Materials·Christopher James HeardPetr Nachtigall

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Methods Mentioned

BETA
scanning
X-ray
transmission electron
electron imaging
NMR
electron microscopy

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