Photoelectron spectroscopy, lead compounds

One way in which cobalt dispersion can be increased is the addition of an organic compound to the cobalt nitrate prior to calcination. Previous work in this area is summarized in Table 1.1. The data are complex, but there are a number of factors that affect the nature of the catalyst prepared. One of these is the cobalt loading. Preparation of catalysts containing low levels of cobalt tends to lead to high concentrations of cobalt-support compounds. For example, Mochizuki et al. [37] used x-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR) to identify cobalt silicate-like species in their 5% Co/Si02 catalysts modified with nitrilotriacetic acid (NTA). The nature of the support also has... 

A second type of synthetic route to meso-ionic l,3,4-thiadiazol-2-imines (247) is based on the acid-catalyzed reaction of N-thioacylhydrazines (232) with aryl isothiocyanates (Ar-NCS). " This reaction yields the s ts (248) as precursors of the meso-ionic heterocycles (247). An interesting variant upon this route involves the reaction between IV-thioacylhydrazines (232) and acyl isothiocyanates (RCO-NCS). This leads to the meso-ionic heterocycles 247, R = COzEt, CONMej, COMe, COCMe, COAr, and SOjPh. The investigation of these compounds by X-ray photoelectron spectroscopy is a good example of the application of this physical method for the examination of meso-ionic compounds. 

Important information on the similarities and differences of germanium, tin and lead compounds was obtained using two mutually complementary types of spectroscopy. Photoelectron spectroscopy is widely used to determine the first (Ip) and subsequent ionization potentials of molecules. According to Koopmans theorem, the Ip is equated with the HOMO energy (equation 18)128. 

Lead is not spectroscopically silent. The absorption spectroscopy, photoelectron spectroscopy, and NMR spectroscopy of Pb(II) compounds have all been extensively studied. These techniques not only provide useful insights into the electronic structure and stmctures of Pb(II) compounds, but have also proven useful in the characterization of lead coordination environments in complex samples (e.g., samples of biological or environmental origin). 

X-ray photoelectron spectroscopy (XPS), or given its other name Electron Spectroscopy for Chemical Analysis (ESCA), uses X-rays to excite photoelectrons. The emitted electron signal is plotted as a spectrum of binding energies. The photon is absorbed by an atom, molecule or solid leading to ionization and the emission of a core electron. Analysis will reveal the composition from a depth of 2 20 atomic layers and the electronic state of the surface region of the sample. XPS has the ability to identify different chemical states resulting from compound formation, which are revealed by the photoelectron peak positions and shapes. 

In order to mimic the properties of a partially fluorinated working chromia catalyst, several model-compound-based studies using an instrumental surface analysis approach have been reported. Laboratory-prepared CrjOj is treated under carefully chosen conditions with a reagent that leads to incorporation of fluorine and the resulting material analyzed, for example, by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES). Although of academic interest, such studies relate to models rather than to real catalysts and are probably some distance from describing the real situation. The approach is illustrated with two examples. 

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