XAS characterization and CO oxidation on δ-alumina supported La, Mn, Co and Fe oxides

δ-Al2O3 supported La, Mn, Co and Fe containing catalysts were prepared by impregnation of δ-Al2O3 with citrate-type precursors and calcination at 1073 K. The catalysts were characterized by X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), X-ray absorption spectroscopy (XAS), and BET specific surface area determination. XRD revealed the presence of δ-Al2O3 in all cases and, at 30 wt.% of metal loading, of other single (α-Mn2O3 and α-Fe2O3) or mixed (LaAlO3, LaMnO3, CoAl2O4 and LaFeO3) oxide phases. XAS suggested the formation of some oxide phases also at lower loading. In particular, all Mn and 10 wt.% La–Mn containing samples revealed the formation of α-Mn2O3, while the 30 wt.% La–Mn bimetallic sample showed the formation of LaMnO3 perovskite. All Co containing samples revealed the presence of CoAl2O4 spinel. Fe containing samples showed the formation of α-Fe2O3, while La–Fe containing ones, that of LaFeO3 perovskite. Catalytic tests of CO oxidation were performed in the temperature range 300–800 K. The sample containing 30 wt.% of La and Mn in the form of LaMnO3 perovskite dispersed on δ-Al2O3 was found the most active among all the examined catalysts. Most of the Co containing catalysts were found active at RT too, but they deactivated rapidly. None of the Fe-based samples was active at RT and these catalysts were found, on average, to be substantially less active than the Mn- and Co-based ones.