Diffuse reflectance ultraviolet

Luan Z, Kevan L. Electron spin resonance and diffuse reflectance ultraviolet-visible spectroscopies of vanadium immobilized at surface titanium centers of titanosihcate... 

The substitution of Ce in Ce02 by Hf results in the formation of ceria-hafnia solid solutions, whose properties in soot oxidation were investigated by Reddy et The order of soot oxidation activity (Ce-Hf > Ce-Zr) was correlated to the number of oxygen vacancy defects as evidenced by Raman studies. Moreover, diffuse reflectance ultraviolet-vis spectroscopy patterns showed that the ceria-hafnia sample had the best resolved band at about 255 nm, which has been characterized as a Ce <— 0 charge transfer transition and correlated to a higher concentration of oxygen vacancy defects. In a recent paper the same group also compared the catalytic activity of pure ceria, ceria-zirconia and ceria-lanthana solid... 

ESC] X-ray diffiaction, Fourie-transform infrared and diffuse reflectance ultraviolet-visible spectroscopy 400-900°C/Fe203-Al203... 

Ultraviolet-visible (UV-vis) diffuse reflectance spectra of supported WOx samples and standard W compounds were obtained with a Varian (Cary 5E) spectrophotometer using polytetrafluoroethylene as a reference. The Kubelka-Munk function was used to convert reflectance measurements into equivalent absorption spectra [12]. Spectral features of surface WOx species were isolated by subtracting from the W0x-Zr02 spectra that of pure Z1O2 with equivalent tetragonal content. All samples were equilibrated with atmospheric humidity before UV-vis measurements. 

The most important methods used in in-situ studies of electrode surfaces are various modifications of reflection spectroscopy in the ultraviolet through infrared regions. For electrochemical applications, the specular reflection (at smooth electrode surfaces) is much more important than the diffuse reflection from matt surfaces. The reflectivity, R, of the electrode/ electrolyte interface is defined by ... 

The metal content analysis of the samples was effected by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES Varian Liberty II Instrument) after microwaves assisted mineralisation in hydrofluoric/hydrochloric acid mixture. Ultraviolet and visible diffuse reflectance spectroscopy (UV-Vis DRS) was carried out in the 200-900 nm range with a Lambda 40 Perkin Elmer spectrophotometer with a BaS04 reflection sphere. HF was used as a reference. Data processing was carried out with Microcal Origin 7.1 software. 

With the exception of single-crystal transmission work, most solids are too opaque to permit the conventional use of ultraviolet/visible (UV/VIS) electronic spectroscopy. As a result, such work must be performed through the use of diffuse reflection techniques [8-10]. Important work has been conducted in which UV/VIS spectroscopy has been used to study the reaction pathways of various solid state reactions. Other applications have been made in the fields of color measurement and color matching, areas which can be of considerable importance when applied to the coloring agents used in formulations. 

The intensities of diffuse reflectance and fluorescence are both distributed over the solid angle according to Lambert s cosine-law. An ultraviolet-visible (UV/VIS)-... 

The progressive increase in the extent of POM reduction, as evidenced by the ultraviolet visible diffuse reflectance (UV-vis DR) spectra of catalysts downloaded after different reaction times during catalyst equilibration. 

Fig. 23. Spectra photoconductivity of poly(p,p -diethynylazobenzene ]), the same after 10 min under ultraviolet irradiation (2) photoelectromotive force (3) absorption in diffuse reflection (4) [95]...

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). 

Spectroscopy. - In the following paragraphs we discuss how various spectroscopy tools have been used to illuminate the rich surface chemistry of supported polynuclear metal complexes. These methods include infrared (both diffuse reflectance and transmission), ultraviolet and visible (UV-Vis), x-ray photoelectron spectroscopy (XPS), and x-ray absorption, near edge spectroscopy s (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy s. 

Fio. 16. Benzene vapor adsorbed at 20°G in vacuo. Curve l on silica-alumina(75 25) curve 2 after ultraviolet irradiation (10 hr) curve 3 on chromatographic alumina after ultraviolet irradiation (10 hr). Diffuse reflection spectra, from Barachevsky and Terenin (101). 

Kortiim and Braun (118) found that a ground-up mixture of silica-gel or AljOs with solid anthracene subjected to ultraviolet irradiation in open air displays very rapidly a new absorption band at 275 m.fi (in diffusely reflected light) and acquires on further exposure a yellow-brown coloration. In similar mixtures with MgO and KCl the photooxygenation of anthracene is much slower, which indicates a specificity of silica gel. It could be spectrally shown that anthraquinone is a primary product giving on further exposure 1,4-dihydroanthraquinone (quinizarine), which could be eluted, producing a red solution with an absorption maximum close to that observed on silica-alumina, as just mentioned above. 

This section summarizes the chemistry of the SC isobutane regeneration process. To understand the nature of the hydrocarbons that remain adsorbed on the surface of the USY zeolite catalyst both before and after SC isobutane regeneration, a series of ex-situ temperature-programmed oxidation (TPO), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and ultraviolet-visible (UV-vis) analyses was performed on samples submitted to different TOS 10 under isobutane/butene reaction conditions. 

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