Please use this identifier to cite or link to this item: http://repositorio.unicamp.br/jspui/handle/REPOSIP/74035
Type: Artigo de periódico
Title: SYNTHESIS AND CHARACTERIZATION OF CHROMIUM SILICALITE
Author: MAMBRIM, JST
PASTORE, HO
DAVANZO, CU
VICHI, EJS
NAKAMURA, O
VARGAS, H
Abstract: Infrared spectroscopy (mid-IR), Si-29 and Al-27 magic angle spinning nuclear magnetic resonance (MAS-NMR), powder X-ray diffraction (PXRD), electron paramagnetic resonance (EPR), and photoacoustic spectroscopy (PAS), in combination, have produced useful information about a series of crystalline MFI-type chromium silicalite, synthesized in a fluoride medium. Aluminum is an impurity and occupies framework sites, as evaluated by the Al-27 MAS-NMR. The mid-IR spectra are very similar to the zeolite ZSM-5 with the addition of a weak band at congruent-to 680 cm-1, which we tentatively assign to symmetric stretching of (Cr-O-Si)n groups. The samples are crystalline materials and have expanded unit cells, as PXRD measurements pointed out. The as-synthesized sample shows a distribution of Cr sites, detected by EPR, comprising structure and channel occlusion sites; the nonstructural sites being extensively oxidized to Cr(VI) species after calcination in the presence of dioxygen. The changes in the photoacoustically measured physical properties, such as nonradiative relaxation time, the thermal diffusivity and optical absorption coefficient of both calcined and noncalcined chromium silicalite samples are also reported.
Editor: Amer Chemical Soc
Rights: fechado
Identifier DOI: 10.1021/cm00026a004
Date Issue: 1993
Appears in Collections:Artigos e Materiais de Revistas Científicas - Unicamp

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