Application of Spectrophotometry to the Study of Catalytic Systems

Nature and Estimation of Functional Groups on Solid Surfaces

“…Colour changes occuring on adsorption of a dye due to proton addition can principally be followed visually. However, in view of the uncertanties of a visual judgment of the colour shown by an adsorbed indicator molecule (particularly when the adsorbent is coloured itself), spectrophotometric methods for qualitative and quantitative studies are to be preferred [355]. Figure 30 compares the solution spectra of benzeneazodiphenylamine (PKa = + 1.5) and its acid form with that obtained for the dye after adsorption on a silica-alumina catalyst containing 12 % A1 2 0 3 .…”

“…The spectra of the physisorbed dyes in their base form are usually obtained when the surface acidity is not sufficient for protonation to occur. An interesting feature of the spectra of physisorbed dyes is a rather large red-shift of the principal bands in the adsorbed state as compared to the dye in solution [355].…”

“…Furthermore, these results were in contradiction to other physical or catalytic measurements. Therefore, spectrophotometry has been applied to ascertain that the adsorbed indicator had an absorption spectrum similar to that of the authentic protonated dye [355,481] (see section II.A.2.a.i). A few new fluorescence indicators were introduced in the place of Hammett indicators [481].…”

Comparison of copper and cobalt exchanged zeolites by ultraviolet–visible and infrared spectroscopies. Adsorption of propene and redox properties

“…In the v(CH) range the spectra resemble those obtained upon adsorption of butenes on silicaalumina,29 butenes and hex-1 -ene on Y zeo1ites30 or of butenylcarbonium ions. 31 The intensity increase for the v(CH) and 6(CH) vibrations, the shifts to lower frequencies of v(CH) and to higher frequencies of S(CH), and finally the fact that v(C=C) is absent, account for electron delocalization over the three carbons.31 Furthermore, the absence of an intense v(C=C) vibration at 1530 cm-l (as for the unsubstituted allylic cation32) and the splitting of the 1380 cm-l band (characteristic of gem-CH333) imply substitution on the terminal carbons.…”

Reaction of carotenes in palm oil with acid

“…Surface Br0nsted acid sites on solid catalysts are well known as active sites for heterogeneously catalyzed reactions involving carbonium ions as intermediates. Polynuclear hydrocarbons, when adsorbed on acidic catalysts, produced blue-green cation radicals as a result of electron transfer between the molecule and the Br~nsted acid sites (16)(17)(18). Adsorption of carotene on montmorillonite clay has been attributed to the formation of surface carotene cations by Sarier and Guiler (19) although in their paper, no physical evidence was presented.…”