[Raman and infrared spectroscopic investigation of SO4(2-)/TiO2 solid acids]

The structure, crystal phase transition and surface acid centers of SO4(2-)/TiO2 solid acids calcined at different temperatures were studied by IR and Raman spectroscopy. The results showed that SO4(2-) is combined with metal ions of TiO2 in a chelating bidentate mode. When the calcination temperature is below 500 degrees C, the samples possess stable structure with anatase as the main crystal phase, and there are two types of acid sites (Lewis and Bronsted acid) on the samples, the amount of B acid is about twice as that of L acid. When the temperature is above 500 degrees C, surface SO4(2-) desorb gradually with increasing calcination temperature, leading to crystal phase transition from anatase to rutile and the surface B acid sites fade away.