TiO2-SiO2 mixed oxide modified with H2SO4II. Acid properties and their SCR reactivity

The acid properties of a series of titania and silica mixed metal oxide samples modified by sulfate ions have been studied by FT-IR adsorbed pyridine. The highest concentration of Bronsted acid sites per unit surface area is obtained in the case of mol% TiO2-SiO2/SO42- and pure TiO2/SO42-, while the number of Lewis acid sites per unit surface area is proportional to TiO2 contents. It is suggested that the interaction of S=O in sulfate complex with bulk TiO2 phase effectively accommodates the electron from the neighbor Ti-O-Ti bond. But, considering that the Bronsted acid sites on 56 mol% TiO2-SiO2/SO42- are decreased as compared with unsulfated sample, it could be suggested that the effect of sulfation on the generation of acid sites also depends on the charge balance of the support and the valence unit in Ti-O-Si bond generated during the formation of mixed oxide. The activity obtained in SCR reaction at 450 degreesC suggests that the oxygen in Ti-C-Ti easily participates in the NH3 activation as compared with Ti-O-Si and Si-O-Si bonds and the addition of sulfate can lead to the high reactivity of SCR, due to the acidity increase. (C) 2002 Published by Elsevier Science B.V