Surface state of sulfated zirconia: the role of the sol–gel reaction parameters

Sulfated zirconia powders have been prepared by following a single-step sol–gel preparative route using zirconium propoxide as the starting compound. Sulfuric acidwas employed both as the sulfating agent and as the catalyst of the polycondensation reaction in the gel formation. Three different series of precursors were obtained by varying the water/alkoxide ratio in the reacting sol–gel mixture. The solvent was removed from the gel by freeze-drying (cryogels). All the sampleswere calcined at three temperatures (840, 890 and 940 K) for the same time length (5 h). XPS analyses of the samples were performed by elaboration of the S 2p, O 1s, Zr 3d and C 1s spectral regions. The liquid-medium catalytic activity of the calcined samples was tested in the esterification reaction of benzoic acid with methanol. The role played by the conditions of the sol–gel reaction in affecting the surface state and the catalytic properties of the powders is discussed.