Framework Fe Ions in Fe-ZSM-5 Zeolite Studied by UV Resonance Raman Spectroscopy and Density Functional Theory Calculations
Keju Sun; Fengtao Fan; Haian Xia; Zhaochi Feng; Weixue Li*; Can Li*.
J. Phys. Chem. C.; 2008; 112(41); 16036-16041.  DOI: 10.1021/jp802955s

Abstract: The transition metal containing zeolites show high selectivity and activity in many catalytic reactions under mild conditions, however, detailed characterization of transition metal site ions and nature of the active sites were remained elusive. Here, we present a study of the framework Fe ions in Fe-ZSM-5 zeolite via interplay between resonance Raman spectroscopy excited by 244 and 532 nm laser lines and density functional theory (DFT) calculations. Raman bands at 1165, 1115, 1005 and 516 cm-1 from the framework iron ions in the framework of Fe-ZSM-5 were observed. Based on the DFT calculations, the bands at 1165, 1115 and 516 cm-1 were attributed to 0(A1), 1(A1) and 2(A1) modes with totally symmetric vibration of FeO4 tetrahedron in Fe-ZSM-5, originated from resonant enhanced Raman scattering, while the band at 1005 cm-1 for 6(T2) was identified as a non-totally symmetric vibration of FeO4 tetrahedron from normal Raman scattering. The present work indicates that the resonance Raman bands at 500 and 1100 cm-1 can be used as the spectral characteristics of the transition metal ions substituted in the framework of zeolites.
Key words: UV resonance Raman spectroscopy, Fe-ZSM-5, zeolites, DFT.