Synthesis and characterization of TiO₂-MgO mixed oxides prepared by the sol-gel method

Titania-magnesia mixed oxides, with magnesia concentrations between 10 and 90 wt%, were prepared by using the sol-gel method with titanium n-butoxide and magnesium ethoxide as precursors. The mixed oxides were characterized with X-ray powder diffraction, BET nitrogen adsorption isotherms, electron spin resonance (ESR), and by testing their catalytic activity for 2-propanol and 2-butanol dehydration. Samples contained periclase, anatase, karooite (MgTi₂O₅), geikielite (MgTiO₃), and qandilite (Mg₂TiO₄). The BET specific surface area varied with magnesia concentration; the samples with 50 wt% MgO had the highest area, 211 m²/g. Samples had paramagnetic centers that produced complex ESR spectra when many crystalline phases coexisted. For 2-propanol and 2-butanol decomposition, the activity and selectivity patterns of the mixed oxides were substantially different to those observed in pure TiO₂ and pure MgO. This singular behavior should be a result of the structural defects created by the substitution of Mg²⁺ ions by Ti⁴⁺ cations in titania lattice, as well as by the interfaces created when several crystalline phases coexisted.