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ZrO2-supported La, Co oxide catalysts with different La, Co loading (2, 6, 8, 12 and 16 wt.% as LaCoO3) were prepared by impregnation of tetragonal ZrO2 with equimolar amounts of La and Co citrate precursors and calcination at 1073 K. The catalysts were characterized by X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and BET specific surface area determination. Catalytic CO oxidation was performed at 298–800 K. XRD revealed the presence of tetragonal zirconia with traces of the monoclinic phase. LaCoO3 perovskite was also detected for loading higher than 6%. XAS experiments suggested that at high loading LaCoO3 and Co3O4 were formed, while at low loading, La, Co oxide species interacting with support, and hard to be structurally defined, prevailed. The catalysis study evidenced that the catalytic activity was due to segregated and highly dispersed cobalt oxide species. [Copyright &y& Elsevier]

Structural, redox and catalytic deep oxidation properties of LaAl1−xMnxO3 (x=0.0, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0) solid solutions prepared by the citrate method and calcined at 1073 K were investigated. XRD analysis showed that all the LaAl1−xMnxO3 samples are single phase perovskite-type solid solutions. Particle sizes and surface areas (SA) are in the 280–1180 A˚ and 4–33 m2 g−1 ranges, respectively. Redox properties and the content of Mn4+ were derived from temperature programmed reduction (TPR) with H2. Two reduction steps are observed by TPR for pure LaMnO3, the first attributed to the reduction of Mn4+ to Mn3+ and the second due to complete reduction of Mn3+ to Mn2+. The presence of Al in the LaAl1−xMnxO3 solid solutions produces a strong promoting effect on the Mn4+→Mn3+ reducibility and inhibits the further reduction to Mn2+. Both for methane combustion and CO oxidation all Mn-containing perovskites are much more active than LaAlO3, so pointing to the essential role of the transition metal ion in developing highly active catalysts. Partial dilution with Al appears to enhance the specific activity of Mn sites for methane combustion. [Copyright &y& Elsevier]

ZrO2-supported La, Mn oxide catalysts with different La, Mn loading (0.7, 2, 4, 6, 12, and 16 wt% as LaMnO3) were prepared by impregnation of tetragonal ZrO2 with equimolar amounts of La and Mn citrate precursors and calcination at 1073 K. The catalysts were characterized by X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and BET specific surface area determination. The redox properties were tested by temperature-programmed reduction (TPR), and the catalytic tests were carried out for methane combustion at 650–1050 K and for CO oxidation at 350–800 K. XRD revealed the presence of tetragonal zirconia with traces of the monoclinic phase. LaMnO3 perovskite was also detected for loading higher than 6%. XAS and TPR experiments suggested that at high loading small crystallites of LaMnO3, not uniformly spread on the zirconia surface, were formed; while at low loading, La, Mn oxide species interacting with the support, and hard to be structurally defined, prevailed. The catalysis study indicated that the presence of a perovskite-like structure is necessary for the development of highly active sites. Dilute catalysts were in fact poorly active even when considering the activity per gram of La, Mn perovskite-like composition. For methane combustion and CO oxidation, similar trends of the activity as a function of the loading point to a similarity of the active sites for the two reactions on the examined catalytic system. [Copyright &y& Elsevier]

Catalytic CO oxidation and CH4 combustion were studied over LaAl1−xFexO3 (0≤x≤1) perovskites prepared by citrate method and calcined at 1073 K. The catalysts were characterised by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), and magnetic susceptibility. Redox properties and the content of Fe4+ were derived from temperature programmed reduction (TPR). XRD analysis showed that all the LaAl1−xFexO3 samples are single-phase perovskite-type oxides. A linear variation of the unit cell parameters with x was observed. Optical and magnetic properties are reported and discussed. Particle sizes and surface areas are in the 280–840 A˚ and 4–6 m2 g−1 ranges, respectively. A very low extent of reduction, due to the Fe4+→Fe3+ process, was found by TPR. XRD analysis performed after TPR experiments showed that iron reduction does not lead to a loss of the perovskite structure. For CO oxidation all the Fe-containing perovskites are substantially more active than LaAlO3, so pointing to the essential role of the transition metal ion in developing highly active catalysts. Isolated mononuclear iron sites seem to be more active. Methane is totally converted to CO2 within 1020 K on all the catalysts. The activity increases with iron content, that is with the number of active sites. However, the activity per iron ion decreases with the iron content up to x=0.5, suggesting that the active sites may contain isolated Fe ions bonded to more easily removable oxygen. [Copyright &y& Elsevier]