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[2009.01.05]

 

From molecular fragments to crystals: A UV Raman spectroscopic study on Fe-ZSM-5 synthesis mechanism

Fengtao Fan, Keju Sun, Zhaochi Feng, Haian Xia, Bo Han, Yuxiang Lian, Pinliang Ying, and Can Li*
 Chem. Eur. J., Full paper.
DOI: 10.1002/chem.200801916

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Abstract£ºThe entire sequence of crystallization events of Fe-ZSM-5 was monitored by UV Raman spectroscopy combined with HRTEM, UV-vis spectra, X-ray diffraction patterns and Periodic DFT calculations. Fe-ZSM-5 was synthesized using an organic-free method to avoid signal interference from the organic template in Raman spectra. The framework irons with the Resonance Raman bands at 516, 1115, and 1165 cm-1 and Raman band at 1016 cm-1 are detected for Fe-ZSM-5. In the early synthesis stage of Fe-ZSM-5, the precursor contains iron atoms in distorted tetrahedral coordination and five- and six-membered silicate rings. Nucleation via aggregation of the precursor species was monitored by UV Raman spectroscopy based on the Resonance Raman effect, and confirmed by Periodic DFT calculations. The unparalleled evolutions of the iron species on the surface and in the bulk phase are detected by UV Raman spectroscopy excited with 244 and 325 nm, confirmed by HRTEM. It is found that the nucleation takes place first in the core of the amorphous particles, and the crystalline nuclei with Fe-ZSM-5 structure are formed in the core by consuming the amorphous shell. Finally the amorphous particles are completely transformed into Fe-ZSM-5 crystals.

Keywords£ºsynthesis mechanism • hydrothermal synthesis • Fe-ZSM-5• zeolite • UV Raman spectroscopy
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