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

Abstract

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.