From molecular fragments
to crystals: A UV Raman spectroscopic study on Fe-ZSM-5
Fengtao Fan, Keju Sun, Zhaochi Feng, Haian Xia, Bo Han, Yuxiang
Lian, Pinliang Ying, and Can Li*
Chem. Eur. J.,
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