Surface acidic properties of sulphated Fe2O3-TiO2

Mixed iron and titanium oxides with varying quantities of sulphate species have been prepared by sulphation of ilmenite followed by calcination. A combined approach involving DFT and DRIFT spectroscopy has been adopted to determine the appropriate structure for adsorption of pyridine on sulphated Fe2O3-TiO2 (SFT). The DRIFT spectra obtained for pyridine adsorbed SFT samples show equal number of Bronsted and Lewis acid sites. The TG-DTG analysis reveals the greater affinity for water and hydroxyl groups on SFT. Evaluation of IR frequencies for various structures based on DFT demonstrates that the adsorption of water/hydroxyl groups on S and/or Fe leads to the conversion of Lewis acid sites into Bronsted acid sites. Investigation of Mulliken charges for Fe, Ti, S and N for the pyridine adsorbed SFT structures demonstrates the preferable adsorption of pyridine on sulphur rather than on Fe.