Surface deposits, identification

Figure Bl.22.1. Reflection-absorption IR spectra (RAIRS) from palladium flat surfaces in the presence of a 1 X 10 Torr 1 1 NO CO mixture at 200 K. Data are shown here for tluee different surfaces, namely, for Pd (100) (bottom) and Pd(l 11) (middle) single crystals and for palladium particles (about 500 A m diameter) deposited on a 100 A diick Si02 film grown on top of a Mo(l 10) single crystal. These experiments illustrate how RAIRS titration experiments can be used for the identification of specific surface sites in supported catalysts. On Pd(lOO) CO and NO each adsorbs on twofold sites, as indicated by their stretching bands at about 1970 and 1670 cm, respectively. On Pd(l 11), on the other hand, the main IR peaks are seen around 1745 for NO (on-top adsorption) and about 1915 for CO (tlueefold coordination). Using those two spectra as references, the data from the supported Pd system can be analysed to obtain estimates of the relative fractions of (100) and (111) planes exposed in the metal particles [26].

The studies dealing with opportunity of photosensibilized formation of 02 from the surface of deposited oxides were studied in a vial similar to that described in [24]. The identification of C>2 was provided by similar techniques. The evaluation of concentration of C>2 molecules in gaseous phase involved the assessment of oxidation rate of 1,3-diphenil-benzofurane in hexadecane. It occurred that in this case the concentration of 02 molecules amounts to 10 cm. ... 

Most major ore deposits that intersect the earth s surface have probably been identified. To satisfy the increasing demand for metals, buried deposits lacking primary surface expressions have become targets for exploration. Future discoveries of economic mineral deposits increasingly rely on the identification of subtle, secondary expressions of deeply buried metal bearing systems (Govett 1976 Kelly et al. 2006). 

The use of surface-enhanced resonance Raman spectroscopy (SERRS) as an identification tool in TLC and HPLC has been investigated in detail. The chemical structures and common names of anionic dyes employed as model compounds are depicted in Fig. 3.88. RP-HPLC separations were performed in an ODS column (100 X 3 mm i.d. particla size 5 pm). The flow rate was 0.7 ml/min and dyes were detected at 500 nm. A heated nitrogen flow (200°C, 3 bar) was employed for spraying the effluent and for evaporating the solvent. Silica and alumina TLC plates were applied as deposition substrates they were moved at a speed of 2 mm/min. Solvents A and B were ammonium acetate-acetic acid buffer (pH = 4.7) containing 25 mM tributylammonium nitrate (TBAN03) and methanol, respectively. The baseline separation of anionic dyes is illustrated in Fig. 3.89. It was established that the limits of identification of the deposited dyes were 10 - 20 ng corresponding to the injected concentrations of 5 - 10 /ig/ml. It was further stated that the combined HPLC-(TLC)-SERRS technique makes possible the safe identification of anionic dyes [150],... 

The identification of a specific zeolite species with a particular genesis or environment of formation is very difficult if natural mineral occurrence is used as the sole criteria. Most alkali zeolites are found at one place or another in most low temperature geological situations. Various authors have cited various physical and chemical factors which would control the sequence or particular species of alkali zeolite found in nature. Silica and alkali activities in solution are of great importance in surface and buried deposits (Sheppard and Gude, 1971 Honda and Muffler, 1970 Hay, 1964 Coombs, t al.. 1959 Read and Eisbacher, 1974). 

The identification of size, shape, and axial ratio can also be done by direct observation in the electron microscope (EM). This is accomplished by depositing single molecules (if they can be obtained) directly on polymer-coated copper grids and then shadowing them with heavy metals or making a replica of the molecular surface on mica. The sample can then be viewed in the transmission EM and photographs can then be taken after calibration of the magnification factor. 

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