Modification of silica gels with small admixtures of titanium ions

Structure of Fumed Titania and Silica/Titania and Influence of the Nature of Surface Sites on Interaction with Water

“…The question arises about the possi- (13)(14)(15)(16) 4 , i.e., the basic propFumed titania or the individual titania phase in ST possess a crystalline structure, but a oxide surface layer can be disor-erties increase faster than the L-acidity as the titania clusters (Table 7) or 014 kJ/mol for other cluster (Table 8), but for (HO) 4 Ti R OH 2 , the energy of interaction is higher. The Ti…”

Active Site Nature of Pyrogenic Alumina/Silica and Water Bound to Surfaces

“…Calculations of the Al 2 O 3 /SiO 2 clusters (Table ) show that the Al atoms are striving to the 4-fold coordinated state for the individual AlO n polyhedrons in the silica matrices as a bond length r Al - O for two ( r MO , r M ← O ) from six bonds between AlO 6 and SiO 4 (or AlO 4 for the alumina cluster) units are longer than an ordinary Al−O bond in Al 2 O 3 . This is observed presumably when the individual alumina phase is absent − (i.e., there is only Al IV ). Water molecules adsorbed on the surface can increase the coordination number of the Al IV atoms to Al VI , when they dissociate forming the ⋮MOH and ⋮M−O(H)−M⋮ groups If this process is impossible, e.g., when all boundary O atoms are already linked with H, than the next H 2 O molecule can form a hydrogen-bonded or donor-acceptor complex …”