Journal
JOURNAL OF PHYSICAL CHEMISTRY C
Volume 113, Issue 19, Pages 8211-8219Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jp900313y
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Funding
- DOE [DEFG0296ER14681]
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Low temperature H-1 MAS NMR spectroscopy is used to study protonic motion in zeolite HZSM-5 in both samples that have been dried using procedures that are standard in the literature and samples that have been more carefully dehydrated. A significant enhancement of proton mobility is seen for the standard dehydrated HZSM-5 sample in comparison to that seen for the much drier sample. This is ascribed to a vehicle-hopping mechanism involving the residual water that is present in these zeolites. A gradual change of the framework structure is observed on cooling to approximately 213 K, as monitored via the change in H-1 chemical shift values of the Bronsted acid resonances and by X-ray diffraction. A more sudden change in structure is seen by differential scanning calorimetry and NMR at approximately 220-230 K, which is associated with changes in both the mobility and the modes of binding of the residual water to the Bronsted acid sites and the zeolite framework.
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