Characterization and reactivity of Mg xFe 2-2xO 3-2x and Mg yZn 1-yFe 2O 4 solid solution spinels prepared through the supercritical drying method

Mixed oxides with the formula Mg xFe 2-2xO 3-2x (0{precedes above single-line equals sign}x<1) and Mg yZn 1-yFe 2O 4 (0{precedes above single-line equals sign}y{precedes above single-line equals sign}1) have been prepared as aerogels (i.e. gels obtained by hydrolysis of metal acetates or alkoxides in methanolic solution followed by drying under supercritical conditions). Mg xFe 2-2xO 3-2x samples with 0<x<0.5 are Mg-deficient spinels, giving rise to MgFe 2O 4+α-Fe 2O 3 mixtures when calcined at 773 K. With x=0.5 the stable phase MgFe 2O 4 is obtained. With 0.5<x{precedes above single-line equals sign}0.66 a Mg-excess spinel phase is obtained that is substantially stable event at 1073 K. Surface areas of the spinel phases range around 100 m 2/g. Mg yZn 1-yFe 2O 4 are stable solid solution spinels in the entire range, and convert progressively from normal to partially inverted spinels by increasing y. The bulk and surface properties of these materials have been, investigated by XRD, TG-DTA, FT-IR and FT-Raman spectroscopies, BET surface areas and SEM microscopy. Also FT-IR spectra of the surface OH groups and catalytic activity in the reduction of NO by NH 3 were investigated. © 1995 Elsevier B.V. All rights reserved.