Laser Raman spectroscopy, characterization

Structural characterization of the surface metal oxide species was obtained by laser Raman spectroscopy under ambient and dehydrated conditions. The laser Raman spectroscope consists of a Spectra Physics Ar" " laser producing 1-100 mW of power measured at the sample. The scattered radiation was focused into a Spex Triplemate spectrometer coupled to a Princeton Applied Research DMA III optical multichannel analyzer. About 100-200 mg of... 

With the aim to study the characteristics of VPO catalysts in the course of butane oxidation to maleic anhydride together with a simultaneous evaluation of the catalytic performance, we have used Raman spectroscopy which is a very sensitive probe for determining the presence of V0P04-like entities together with (VO)2P207. An in situ Laser Raman Spectroscopy (LRS) cell was built in our laboratory (6). In the corresponding publication (6 ), the preparation and the characterization by XRD, Ip... 

Some very important surface properties of solids can be properly characterized only by certain wet chemical techniques, some of which are currently under rapid improvement. Studies of adsorption from solution allow determination of the surface density of adsorbing sites, and the characterization of the surface forces involved (the energy of dispersion forces, the strength of acidic or basic sites and the surface density of coul-ombic charge). Adsorption studies can now be extended with some newer spectroscopic tools (Fourier-transform infra-red spectroscopy, laser Raman spectroscopy, and solid NMR spectroscopy), as well as convenient modern versions of older techniques (Doppler electrophoresis, flow microcalorimetry, and automated ellipsometry). 

Table VI A comparison of Infrared and Laser Raman Spectroscopy for the Characterization of solid/liquid Interfaces...

Although several metal-containing heterocyclic compounds (such as porphyrins, phthalocyanines, naphthenates) are present in oil fractions most of the bench-scale research has been based on relatively rapid Ni, V, or Ni/V deposition procedures in which experimental FCC formulations have been artificially metal contaminated with solutions of Ni and/or V naphthenate dissolved in benzene (or toluene) (24). Metal levels in these novel FCC are usually above 0.5% that is well above the concentration that today exist on equilibrium FCC, see Figure 1. High metal concentration facilitate the study and characterization of Ni and V effects by modern characterization techniques such as X-ray photoelectron spectroscopy (XPS), Laser Raman spectroscopy (LRS), X-ray diffraction (XRD), electron microscopy, secondary ion mass spectrometry (SIMS), and 51V nuclear magnetic resonance (NMR). 

Laser Raman spectroscopy complements ssNMR in characterizing the different types of carbonaceous structures formed in the charred materials. Indeed, in the Raman spectra of graphite, there are many features that can be identified and that can provide information about the properties of the materials, such as their electronic structure as well as information about imperfections or defects. Since mechanical, elastic, and thermal properties of graphite are influenced by its structure, Raman spectra could provide interesting information regarding the carbonization process.1617... 

The simultaneous application of EPR/ultraviolet-visible diffuse reflectance spectroscopy (UV-vis-DRS)/online gas chromatography (GC) to characterize working catalysts was realized a few years ago 14), and laser-Raman spectroscopy has recently been coupled with these to provide the first such simultaneous application of three techniques 15). 

The following techniques for the characterization of supported vanadia catalysts and vanadia will briefly reviewed temperature programmed reduction (TPR) [26, 30], oxidation (TPO) [30] and desorption (TPD) [33, 36, 41, 44] laser Raman spectroscopy (LSR) [5, 25, 35, 36, 39, 44] Fourier-transform infrared spectroscopy... 

In this study, suboxides of vanadia catalysts were used in pentane, pentene, dicyclopentadiene and cyclopentane oxidation reactions. In the previous phase of the work [12,13], the role of alkali promoters on the catalyst selectivity was examined. The catalysts were reduced in situ at different temperatures and the effect of pre-reduction temperature was investigated. Controlled-atmosphere characterization of pre-reduction, post-reduction, and post-reaction catalysts were performed using X-ray diffraction. X-ray photoelectron spectroscopy, laser Raman spectroscopy and temperature-programmed desorption experiments. The objectives of this study were to determine the activity and selectivity of different suboxides of vanadia in... 

Zeolitization reactions have been found to predominate in the low-temperature hydrothermal reactions of metakaolinite, Al2Si207. The reactions have been carried out with and without additions of silica by use of bases LiOH, NaOH, RbOH, and CsOH and also the mixtures NaOH + LiOH, NaOH + KOH, KOH + LiOH, and NaOH -I- Me4NOH. The zeolites produced, which have been characterized by a number of physicochemical techniques, have been listed in the section on aluminosilicates (Table 40). The synthesis of the zeolites Linde A and faujasite has been studied using phosphorescence spectroscopy and laser Raman spectroscopy the results obtained were indicative of a zeolite crystallization in the solid gel phase via condensation between hydroxylated Si— Al tetrahedra. 

Molecular Characterization of Dieiectric Fiims by Laser Raman Spectroscopy... 

Laser Raman spectroscopy has been applied to materials characterization studies over the past several years. Annual reviews discuss advances in the field and provide references for a number of specialized areas including thin film analysis (1). The attractive features for using Raman spectroscopy to evaluate thin films include a nondestructive j n situ measurement capability plus the ability to acquire both spatially and time-resolved vibrational data from which structural information can be inferred. 

Raman (Laser)Raman spectroscopy Identification/stmcture of species, characterization especially in the low-frequency range... 

Melanitis N, Tetlow PL, Galiotis C, Characterization of PAN based carbon fibres with laser Raman spectroscopy. 1. Effect of processing variables on Raman band profiles, J Mater Sci, 31(4), 851-860, 1996. 

Several analytical techniques are used to characterized carbon materials such as diamond and DLC. These include x-ray diffraction, transmission electron microscopy, electron-energy-loss spectroscopy (EELS), and laser-Raman spectroscopy, the last two techniques being probably the most frequently used. 

As mentioned in Ch. 11, Sec. 2.1, laser-Raman spectroscopy is used extensively to detect the diamond structure. It is also useful to characterize... 

Centi, G. (1993). Vanadyl Pyrophosphate A Critical Overview, Catal. Today, 16, pp. 5-26. Ben Abdelouahah, F., Olier, R., Guilhaume, N., et al. (1992). A Study By In Situ Laser Raman Spectroscopy of VPO Catalysts for n-Butane Oxidation to Maleic Anhydride I. Preparation and Characterization of Pure Reference Phases, J. Catal., 134, pp. 151-167. 

Ben Abdelouahab F.B., Olier R., Guilhaume N., Lefebvre F. and Volta J.-C. (1992). A study by in situ laser Raman spectroscopy of VPO catalysts for n-butane oxidation to maleic anhydride. I. Preparation and characterization of pure reference phases, J. Catal, 134, 151-167 Benabde-louahab F.B., Volta J.-C. and Olier R. (1994). New Insights into VOPO4 Phases Through Then-Hydration, J. Catal, 148, pp. 334-340. 

GE McGraw, Investigation of polyester structure by laser Raman spectroscopy. In CD Craver, ed. Polymer Characterization Interdisciplinary Approaches. New York Plenum Press, 1971, pp 37-46. 

H.-B. Zhang and G. L. Schrader, Characterization of a fused iron catalyst for Fischer-Tropsch synthesis by in situ laser Raman spectroscopy, Journal of Catalysis, vol. 95, no. 1, pp. 325-332, 1985. 

Perhaps the best known and most used optical spectroscopy which relies on the use of lasers is Raman spectroscopy. Because Raman spectroscopy is based on the inelastic scattering of photons, the signals are usually weak, and are often masked by fluorescence and/or Rayleigh scattering processes. The interest in usmg Raman for the vibrational characterization of surfaces arises from the fact that the teclmique can be used in situ under non-vacuum enviromnents, and also because it follows selection rules that complement those of IR spectroscopy. 

An interesting variation of Raman spectroscopy is coherent anti-Stokes Raman spectroscopy (CARS) (99). If two laser beams, with angular frequencies CO and CO2 are combined in a material, and if cjj — is close to a Raman active frequency of the material, then radiation at a new frequency CJ3 = 2cJ2 — may be produced. Detection of this radiation can be used to characterize the material. Often one input frequency is fixed and the other frequency, from a tunable laser, varied until matches the Raman frequency. CARS has the capabiHty for measurements in flames, plasmas, and... 

The crystalline mineral silicates have been well characterized and their diversity of stmcture thoroughly presented (2). The stmctures of siHcate glasses and solutions can be investigated through potentiometric and dye adsorption studies, chemical derivatization and gas chromatography, and laser Raman, infrared (ftir), and Si Fourier transform nuclear magnetic resonance ( Si ft-nmr) spectroscopy. References 3—6 contain reviews of the general chemical and physical properties of siHcate materials. 

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