Alumina Optical absorption

Very recently, Bailey and Richards (23) have shown that a high degree of sensitivity for adsorbed species can be achieved by measuring the absorption of infrared radiation on a thin sample cooled to liquid helium temperature. The optical arrangement used in these studies is shown in Figure 10. The modulated beam produced by the interferometer is introduced into the UHV sample chamber and reflected off a thin slice of monocrystalline alumina covered on one side by a 1000 k film of nickel or copper. Radiation absorbed by the sample is detected by a doped germanium resistance thermometer. The minimum absorbed power detected by this device when operated at liquid helium temperature is 5 x 10 14 W for a 1 Hz band width. With this sensitivity absorbtivities of 10"4 could be measured. 

The interaction of cupric ions with alumina supports has subsequently been studied more extensively as a function of the support surface area, metal loading, and calcination temperature (93,279) by means of EXAFS and X-ray absorption-edge shifts, in conjunction with XRD, EPR, XPS, and optical reflectance spectroscopy. These techniques, each sensitive to certain structural and electronic aspects, allow a unified picture of the phases present and the cation site location. Four Cu2 + ion sites are distinguished in the catalysts. In low concentrations (typically below about 4 wt. % Cu/100 m2/g support surface area) Cu2 + ions enter the defect spinel lattice of the A1203 support. The well-dispersed surface copper aluminate has Cu2+ ions predominantly occupying tetragonally (Jahn-Teller) distorted octahedral sites, although... 

The difference between these results must be ascribed to the difference in composition, since the light sources and conditions of illumination were similar. However, there is no evidence beside that of the catalytic activity to demonstrate any difference between the centers in the two materials. The optical spectra (diffuse reflectance) (68, 88) were closely similar, as expected from the role of alumina impurity in silica gel, and adequate data are not available from ESR for silica-alumina. Only slight differences in absorption spectrum might be necessary the reversal of the effect on activity around 3000 A in silica gel might well be shifted to another wavelength in silica-alumina. 

The crystal field optical transitions of Cr + in an octahedral site are shown in Fig. 26. The splitting of the upper energy levels by the weak trigonal distortion ( 350 cm ) (67,168-170) of the octahedron cannot be resolved in powder samples of chromia-alumina. The optical reflectance spectra shown in Fig. 27 show a gradual shift of the absorption maxima near 17,000 and 23,000 cm (15,39,171) due to the lattice expansion that results when chromia is added to an alumina lattice. The optical spectra conform to the Tanabe and Sugano (168,172-174) theoretical calculations. The Racah parameter varied with the chromium content (15,171), Variable temperature (169,175) and variable pressure (176,177) optical spectra have been obtained for ruby samples. 

Nippon Shokubai Kagaku Kogyo disclosed a complementary process for the synthesis of optically active cyanohydrins. (S)-hydroxynitrile lyase derived from plants like Euphorbiaceae, Gramineae, and Olacaceae could successfully be applied to synthesize 99.9% optically active (S)-mandelonitrile (S)-175 [147]. The enzymes showed high absorption ratios when immobilized on porous inorganic material such as ceramics, silica, alumina, or silica/alumina zeolithes and were also used for the synthesis of other cyanohydrins. 

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