
147Sulfated Inorganic Oxides for Methyl Esters Production
No spectra will be reported for the sake of brevity, as all SnO
2
-TiO
2
samples
exhibit almost the same trend, both in the background prole and in the differential
spectral features obtained for CO adsorption. In summary, it can be reported that
(i) Surface sulfate groups exhibit the spectral features typical of covalent spe-
cies, as reported in the literature so far (Sarzanini et al., 1995), and, as a
function of the increasing TiO
2
content, the presence of polynuclear sulfate
groups is evident;
(ii) Lewis acidity, as tested by CO adsorption at room temperature, is present in
ver