Mesoporous Aerogels and Xerogls Based on Sulphated Zirconia Doped with Cobalt as Hexane Isomerization Catalysts

The sol-gel method was used to synthetize catalysts based on sulphated zirconia doped with cobalt. The effect of the drying mode on the properties of those solids was studied by several techniques of characterization such as XRD, physisorption of azote, UV-visible, IR and XPS spectroscopies. Our results show that the evacuation of the solvent on its supercritical conditions ensures the cristallinty of this material on the ZrO2 tetragonal phase at low calcination temperature. The IR spectroscopy showed that those conditions permit also a better retention of active sulphate groups. UV-visible and XPS spectroscopies revealed that the oxidation state of cobalt is different in the two types of solids. On the aerogels, cobalt is present as Co (III). However, on xerogels, the oxidation state appears only at high calcination temperature. The fact induces different catalytic behaviour of those solids in the reaction of n-hexane isomerisation. Only solids with cobalt in the oxidation state +3 are active and the others are inactive.