Infrared spectroscopy (mid-IR), 29Si and 27Al 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 27Al MAS-NMR. The mid-IR spectra are very similar to the zeolite ZSM-5 with the addition of a weak band at ~6 8 0 cm-l, which we tentatively assign to symmetric stretching of (Cr-0-Si), 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(V1) 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.
1.23 : 1 and Of formula Na~6Al8~Silo6038, * 250HzO. The
X-Ray analysisThe crystalline structure of the samples was established by X-ray diffraction using a Siemens D-500 diffractometer monitored at 35 kV and 15 mA, with Cu-Ka radiation (A = 0.15406 nm) at a scan speed of 1 degrees min-' (in 28)with Diffrac-AT software [version 3.2, SOCABIM (1993)l with a sample surface area of 6.45 cm2; JCPDS PDF 41-1049 for CdS was used to reference the peaks.
PA techniqueThe PA effect looks directly at heat generated in a sample due to non-radiative deexcitation processes following the absorp-
Chemical and X-ray diffraction analysisThe parameter q was fixed to values of 0.05, 0.10, 0.20, 0.50 and 0.80. Fig. 3(a) and (b) illustrate the plot of number of Cd 2652
Este texto tem o objetivo de mostrar que a condutividade não é um fenômeno exclusivamente elétrico ou eletrônico. Outros carregadores de cargas, os íons, podem gerar condução quando se movimentam em um retículo sólido, obedecendo a condições estruturais muito específicas.
Zeolites are framework aluminosilicates extensively used in industry. The quest for cheap high-quality chemicals added to the growing concern with the planet's environmental conditions have stimulated continuous development and upgrading of resources for materials syntheses. In this work, zeolites from MFI, LTA and FAU groups, largely applied indystrially, were synthetized from mineral Al-rich residues.
This work reports the transformation of a layered aluminophosphate (AlPO-CJ70) with N,N-dimethylbenzylamine as SDA and inorganic layers containing two different Al sites and three P sites, where two of them are ≡P=O sites and the other is a =P(OH)=O group, in three dimensional silicoaluminophosphates with structures analogous to SAPO-5 and SAPO-15. The synthetic process of the 3D materials are different. The SAPO-5 analogue, called UEC-4, was synthesized in an aqueous media in the presence of TEABr and silica, and the SAPO-15 analogue, UEC-5, was synthetised by a dry-gel conversion method in the presence of n-butylamine and silica. Both materials were characterized with powder X-rays diffraction, solid state nuclear magnetic ressonance, infrared spectroscopy, scanning electron microscopy and termogravimetry.
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