Study of acidity of aerogels ZrO2-SO42- by isopropanol dehydration reaction, surface potential and X-ray photoelectron spectroscopy

Sulphated zirconia aerogels, with definite atomic ratio S/Zr and hydrolysis ratio (H = H2O/Zr) were prepared by the autoclave method. The addition of sulphate ions causes a decrease of the cristallinity of zirconia. XPS resul ts show the O1s photoelectronpeak which could be decomposed in two componen ts for the reticular oxygen of the zirconia framework and for oxygen attrib uted to the OH groups and/or sulphates groups, and the S2p photopeak charac teristic of sulphates species. The Kelvin probe shows that the value of pur e zirconia is around 200 mV. This value grows up to 1200 mV for sulphate do ped catalysts. The modification of the work function is probably due to the charge transfer from the zirconium to an oxygen species, responsible for t he increase of Lewis acidity. The catalysts prepared with hydrolysis ratio of H = 4 exhibit higher activities in the isopropanol dehydration reaction than those with H = 2 in the temperature range 373 K-423 K.