Characterization of alumina-titania mixed oxide supports I. TiO2-based supports

The bulk and surface properties of a series of titanium-rich Al₂O₃-TiO₂ mixed oxides catalytic supports have been determined by different techniques (S_BET, pore size distribution, XRD, DTA, FTIR, FT-Raman, UV-vis diffuse reflectance and FTIR of adsorbed pivalonitrile and pyridine). The analysis of the results indicates that the prepared solids were fairly homogeneous, with titania showing the anatase structure and no segregation of alumina particles. Also, the addition of small amounts of alumina to titania enhances significantly its thermal stability. The UV, FTIR, Raman and XRD results suggest that part of the alumina forms a solid solution with TiO₂ and that two types of aluminum are present, one due to surface monolayer-type species and other due to octahedrally coordinated bulk species. The FT-Raman and the FTIR spectra of adsorbed probe molecules support the idea that the anatase particles are largely covered by surface alumina partial monolayers.