Mesoporous Mossbauer spectroscopy

Mesoporous tin-containing analogues of MCM-41 and tin oxide-modified me-soporous SBA-15 have also been characterized by Mossbauer spectroscopy (162,163). In the first case, the results suggest that tin was incorporated in the structure of the silicate and, in the second, they indicated that two types of supported tin species were formed, depending on the tin content. One would correspond to atomically isolated species stabilized in the wall of the pore and susceptible to reduction to Sn under reductive treatment conditions and the other to large oxide clusters distributed in the external pore structure. 

With the development of nanoscaled catalysts, several recent studies have pointed out the great interest of recording Mossbauer spectra below 4.2 K up to 0.055 K (100,203,204) it allowed the identification at the surface of various support such as mesoporous silica or Zr02, the formation of nanometric iron oxide clusters this identification was not possible in classical low temperature studies conducted above 4.2K, which concluded to the presence of larger particles. The analysis by Mossbauer spectroscopy performed at lower temperature enabled to show that these larger particles were agglomerates of nanometric iron clusters and allowed to reach another level of resolution of ferric particles structures (204). 

Iron oxide nanoclusters were synthesized within mesoporous MCM-41 doped with aluminum using evaporation-condensation of volatile Fe(CO)5 [53]. Subsequent calcination in an O2 flow resulted in amorphous y-Fe203 particles with diameters of 2-3 nm evenly distributed through the well-defined hexago-nally packed cyhndrical pores. These results were sohdly confirmed by combination of Mossbauer spectroscopy, XRD, TEM, and STEM (Fig. 4). 

Morphology, effect on diffusion Morphology, mesoporous silica Morphology, MFl Morphology, MFI, internal Mossbauer spectroscopy MPV (Meerwein-Ponndorf-Verley) reduction... 

High-surface-area mesoporous CuO- Fc203 catalysts with various CuO content (denoted as FeCuX, X=10, 15, 20, 33, 50 mol.%,) were prepared by a surfactant-assisted method of nanocrystalline particle assembly. The method is described in details in Ref [4]. All samples were characterized by XRD, N2 adsorption, TEM, H2-TPR and Mdssbauer spectroscopy. Mossbauer spectra (MS) were obtained with a Wissel electromechanical Mdssbauer spectrometer (Wissenschaftliche Elektronik GmbH, Germany) working at a... 

---