Formation and characterization of a SnO2–Al2O3 system derived from a sol–gel process based on different tin precursors

A series of SnO2–Al2O3 samples with SnO2 to Al2O3 molar ratio of 1:1, 0.5:1, 0.25:1 and 0.1:1, have been synthesized by the sol–gel technique using Al(C3H7O)3 and tin (IV) dihydroxy 2,4-pentanedione acetate as precursors. Samples of the above series were characterized by thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy and nitrogen adsorption to establish their porous structure. The structures of the binary gel systems obtained were found to differ from those of the analogous series in which Sn(ac)4 (acetic series) was used as precursor. The tin component introduced into the samples of both series was responsible for the narrowing of the range of diameters of the pores (contributing to the highest extent to the cumulative pore volume) relative to their range in pure aluminum gel. The range of the dominant pore diameters was at the same time shifted towards smaller values, but these changes were more pronounced for (ac) series. The use of β-diketonate complexes of tin instead of Sn(ac)4, leads also to changes in the character of OH group on the surface of the binary gel samples. For this series (acac) of binary gels in the whole range of concentrations of the tin component only one type of hydroxyl groups appears, not present in the monocomponent aluminum gel and in the binary gels of (ac) series.