Characterization of sulfated TiO2 prepared by the sol–gel method and its catalytic activity in the n-hexane isomerization reaction

Abstract

Sulfated TiO2 was prepared by a single-step sol–gel method, in which the hydrolysis and sulfation occur in the same step, varying some conditions of the preparation method. The characterization was carried out by thermogravimetric analysis, infrared absorption spectroscopy, Raman spectroscopy, pyridine adsorption infrared spectroscopy for the determination of the Brönsted acid sites/Lewis acid sites ratio, determination of the specific surface area (BET method), average pore diameter (BJH method) and catalytic activity in the n-hexane isomerization reaction. In the infrared spectra it was verified that the sulfate is coordinated to the titanium in a chelate form, while in the Raman spectra it was observed that the samples are in an anatase crystalline form. Catalytic tests of the n-hexane conversion at 100 and 200 °C were carried out. At 100 °C, it was observed that the selectivity for isomerization and catalytic stability are higher than at 200 °C, however, at 100 °C the conversion is lower than at 200 °C. Among the structural and textural properties investigated, it was found that the samples which had greater average pore diameters and a higher Brönsted acid sites/Lewis acid sites ratio were the ones which showed greater catalytic activity.