Structure and Lewis acid properties of gallia–alumina catalysts

The surface structure of Ga2O3–Al2O3 catalysts was investigated by IR and ESR spectroscopy. As a result of modification by gallia, alumina hydroxyl cover changes significantly. The new band 3680–3688 cmy1 ascribed to bridging structure Ga`OH`Al has been observed. By means of IR spectroscopy, adsorbed CO and ESR with anthraquinone as a probe molecule, two types of Lewis acid sites and their concentration were defined. These sites are coordinately unsaturated aluminium cation Al3cuqs and coordinately unsaturated gallium cation Ga3cqus. In the case of Ga2O3–Al2O3 catalysts with a gallia content of 1–10 mol%, surface Lewis acid properties are in accordance with the assumption of solid solution formation. Only under significantly non-equilibrium conditions large excess of dopant — 20 mol% Ga2O3–Al2O3, relatively low temperature of calcination y720 K, short time of interaction — 4 h. it becomes possible to stabilize highly dispersed state of gallium oxide, for which the characteristic feature is high concentration and local regulation of Ga3cqus on the surface. It was shown that on the alumina surface there are favourable more than in the case of pure gallia.conditions for the Ga3cqus formation. q2000 Elsevier Science B.V. All rights reserved.