Raman spectroscopic study of supported chromium(vi) oxide catalysts

Viscosity Property and Structure Analysis of FeO–SiO₂–V₂O₃–TiO₂–Cr₂O₃ Slags

“…In the first case, the presence of a shoulder at about 745 cm − 1 was considered due to the symmetric stretching vibration of Cr-O-Cr. 32,33) In the lower wavenumber region, a band at about 439 cm 1 was observed and assigned to be the antisymmetric stretching modes of Cr-O-Cr. 32,33) The plenty of the Cr-O-Cr bonds were consequence of the constraints imposed by their membership of a ring structure, which included Cr-O-Cr, V-O-V, and Si-O-Si bonds.…”

“…32,33) In the lower wavenumber region, a band at about 439 cm 1 was observed and assigned to be the antisymmetric stretching modes of Cr-O-Cr. 32,33) The plenty of the Cr-O-Cr bonds were consequence of the constraints imposed by their membership of a ring structure, which included Cr-O-Cr, V-O-V, and Si-O-Si bonds. 34) Meanwhile, Dines's revealed that SiO 2 could stabilize the supported Cr 3 + in tetrahedral coordination to enhance the ring structure.…”

“…34) Meanwhile, Dines's revealed that SiO 2 could stabilize the supported Cr 3 + in tetrahedral coordination to enhance the ring structure. 32,35) The band at 258 cm − 1 observed for this slag could probably be attributed to the bending/deformation modes of the [Cr 3 + O 6 ] units in the structure. In the second series, the spectrum of pure FeCr 2 O 4 shows well-defined peaks at about 1 030, 737, 677, 516, 595, 495, and 250 cm − 1 , 33,36) so the results are consistent with the XRD and SEM/EDS analysis.…”

The Nature of Surface CrOx Sites on SiO2 in Different Environments

“…The Raman spectra gave well-resolved bands at 394 (m), 987 (s) and 1014 (m) cm -1 with the 394 and 1014 cm -1 bands previously not observed due to strong sample fluorescence with lasers using 514 and 532 nm excitation. The band at 987 cm -1 was assigned to the m s (O=Cr=O) stretching, the band at 394 cm -1 to d(O=Cr=O) bending, and the band at 1014 cm -1 to m as (O=Cr=O) stretching, as suggested by the DFT calculations of Dines et al [17]. Groppo et al, however, had some concern about the assignment of the 1014 cm -1 band because it was stronger than expected and suggested that there may be some heterogeneity of the surface sites.…”

Catalytic upgrading of refinery cracked products by trans-hydrogenation: a review

“…Chromia catalysts have been subject to extensive characterisation using a variety of techniques such as electron spin resonance (ESR) [40,41], infrared spectroscopy (IR) [42,43], diffuse reflectance spectroscopy (DRS) [44,45], photon electron spectroscopy (XPS) [46,47], X-ray diffraction (XRD) [48][49][50], thermo-gravimetric analysis (TGA) [49,50] and Raman spectroscopy [51,52]. Although in the as-prepared catalyst chromia is often in a 6?…”