Chromium oxide supported on zirconium- and lanthanum-doped mesoporous silica for oxidative dehydrogenation of propane

Two series of supported chromium oxide catalysts (1-5 wt.% Cr) have been prepared by using two different mesoporous MCM-41-type solids, zirconium- and lanthanum-doped silica, as supports. These catalysts have been fully characterised in order to correlate their superficial properties, mainly the nature of the chromium species and the acidity, with the catalytic behaviour in the oxidative dehydrogenation of propane, between 350 and 550 degreesC. The partial substitution of Cr(III) ions by aluminium or gallium in the supported chromium oxide reveals that the enhancement of the concentration of Bronsted acid centres due to aluminium ions favours the selectivity to propene, whereas gallium increased the number of Lewis acid sites and the oxidising power of this catalyst. The lower catalytic activity of chromium oxide supported on lanthanum-doped silica has been attributed to the formation of polymerised chromate species, which are less active in the ODH of propane. (C) 2001 Elsevier Science B.V. All rights reserved.