Structural and textural characterization of sol-gel prepared nanoscale titanium-chromium mixed oxides

Chromium-titanium mixed oxides with Cr/Ti+Cr molar ratio of 0.1, 0.2, 0.5, and 0.9 were prepared by a direct sol-gel method. The products were characterized by powder XRD, FT-IR spectroscopy, TEM, and N₂ adsorption. Starting with 10% Cr³⁺, Cr/Ti+Cr=0.1, resulted in a complete dispersion of the Cr³⁺ ions in the titania matrix. On the other hand, a ratio of 0.2 resulted in the formation of traces of segregated α-Cr₂O₃, besides Cr-doped titania. At higher Cr contents, %Cr of ≥50, crystalline Ti-doped Cr₂O₃ and an amorphous Crdoped titania were obtained. Compared with the corresponding one-metal oxides, TiO₂ and α-Cr₂O₃, the mixed oxides showed significantly modified textural properties presented in higher surface areas, larger porosities, and more homogeneous mesoporous structures. In addition, the incorporation of Cr³⁺ ions in the titania lattice enhanced the thermal stability of the anatase phase against transformation to rutile.