Structure and Lewis acid properties of gallia-alumina catalysts

The surface structure of Ga2O3-Al2O3 catalysts was investigated by TR and E SR spectroscopy. As a result of modification by gallia, alumina hydroxyl co ver changes significantly. The new band 3680-3688 cm(-1) ascribed to bridgi ng structure Ga-OH-Al has been observed. By means of IR spectroscopy, adsor bed CO and ESR with anthraquinone as a probe molecule, two types of Lewis a cid sites and their concentration were defined. These sites are coordinatel y unsaturated aluminium cation Al-cus(3+) and coordinately unsaturated gall ium cation Ga-cus(3+). In the case of Ga2O3-Al2O3 catalysts with a gallia c ontent of 1-10 mol%, surface Lewis acid properties are in accordance with t he assumption of solid solution formation. Only under significantly non-equ ilibrium conditions (large excess of dopant - 20 mol% Ga2O3-Al2O3, relative ly low temperature of calcination -720 K, short time of interaction - 4 h) it becomes possible to stabilize highly dispersed state of gallium oxide, f or which the characteristic feature is high concentration and local regulat ion of Ga-cus(3+) on the surface. it was shown that on the alumina surface there an favourable (more than in the case of pure gallia) conditions for t he Ga-cus(3+) formation. (C) 2000 Elsevier Science B.V. All rights reserved .