The development of strong acidity by non-framework aluminum in H-USY determined by Al XAFS spectroscopy
- Utrecht Univ. (Netherlands)
- AMOCO, Naperville, IL (United States)
The local structure of framework and non-framework Al in dealuminated, ultrastable H-Y (H-USY) zeolite has been determined by low energy Al XAFS spectroscopy. By determining the fraction of lattice Al from 27 Al NMR and XRD, the Al-O distances of both structural (tetrahedral) and non-structural (octahedral) Al can be determined. Compared to an Al-O distance of 1.69 {Angstrom} in H-Y, steam dealumination results in a slight decrease in the tetrahedral Al-O distance to 1.67 {Angstrom}. In addition, the octahedral Al-O distance in H-Y is 1.91 {Angstrom} and decreases to 1.84 {Angstrom} in H-USY. A large increase in the intensity of the whiteline in H-USY indicates that the lattice Al has a higher positive charge than in H-Y. The XAFS results suggest that steam dealumination results in the formation of octahedral, non-framework Al at ion exchanged sites which withdraw electron density from the tetrahedral Al through the lattice oxygen ions. The results of this study, support the model that non-framework Al cations withdraw electron density from the lattice oxygen increasing the strength of the acid sites.
- OSTI ID:
- 468018
- Report Number(s):
- CONF-960652--
- Country of Publication:
- United States
- Language:
- English
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