Synthesis, characterization and catalytic properties of titania–silica catalysts

The preparation of titania doped (0.63–3.2 mmol g−1) silica (TiO2/SiO2) was described together with a mixed oxide sample (TiO2–SiO2) at a nominal molar ratio near to 1. These materials were thoroughly characterized by XRD, N2 adsorption at 76 K and ammonia adsorption measurements as well as FTIR spectroscopy. The activity of the materials towards 1-butene isomerization was also tested. FTIR results showed a band at 612 cm−1 attributed to bulk TiO2 phase, in the doped 3.2 mmol g−1 TiO2/SiO2 sample, that was paralleled to an exhibited perturbation for the SiO2 bands in the low frequency region, specifically those at 470 and 808 cm−1. The former band was similarly obtained in the TiO2–SiO2 sample, with a lower decrease in intensity, together with the appearance of a new band at 948 cm−1 attributed to Ti–O–Si linkages. This deed indicated the decrease in population of Ti–O–Ti bridges in the mixed oxide sample. FTIR spectra of adsorbed D2O established the presence of different types of titania hydroxyl groups (3615 and 3520 cm−1) that were composed during desorption of water from the titania surface. The activity towards 1-butene isomeriztion was found to increase gradually, in the doped samples, to achieve its maximum at the titania loading 3.2 mmol g−1, however, a tremendous decrease was obtained for the mixed oxide sample. This behavior was correlated with the acidity of the samples. The dependence of the reaction on either Ti–O–Ti or Ti–O–Si sites was evaluated and discussed.