H-1-NMR SPECTROSCOPY OF TITANIA - CHEMICAL-SHIFT ASSIGNMENTS FOR HYDROXY-GROUPS IN CRYSTALLINE AND AMORPHOUS FORMS OF TIO2

H-1 magnetic-angle spinning (MAS) NMR measurements have been performed on a number of crystalline titanias, and on amorphous silica-supporte d titania and titania-silica, with the aim of measuring the characteri stic proton chemical shifts of hydroxy groups bound to titanias of dif ferent crystalline form. in the case of anatase, signals observed at d elta = 2.3 and 6.7 ppm correspond to terminal and bridging hydroxy gro ups, the results of deuterium exchange experiments (using D2O) and IR data supporting these assignments. For rutile, signals observed at del ta = 2.2 and 5.3 ppm are similarly assigned. Hydroxy groups bound to a morphous titania supported on silica (containing tetrahedrally coordin ated Ti-IV) are found to possess a characteristic chemical shift of de lta = 3.3 ppm. Deconvolution of H-1 NMR spectra of titania-silica (con taining 8 wt% Ti) indicate the presence of a signal at delta approxima te to 3.3 ppm, which is similarly assigned to hydroxy groups bound to tetrahedrally coordinated Ti-IV, together with signals assigned to ana tase and silanol groups. These observations are consistent with litera ture reports indicating the presence of two main titania phases in tit ania-silicas: an amorphous phase containing isolated Ti sites tetrahed rally coordinated by Si-O and OH groups, and segregated nanodomains of TiO2 (anatase or rutile).