Structural and morphological properties of Co-La catalysts supported on alumina/lanthana for hydrocarbons oxidation

Two Al2O3(24wt%)–La2O3(76wt%) supported Co–La oxides with Co loading 4wt% and different La content (1 and 9wt%) were prepared by co-impregnation of the support, the aluminum–lanthanum oxide, with cobalt and lanthanum nitrates in aqueous solution and successive calcination at 800C for 4h. The alumina–lanthana was synthesized by the sol–gel method. The samples were characterized by X-ray diffraction (XRD) and Rietveld refinement in order to identify the crystalline phases and their relative weight. H2-TPR (Temperature Programmed Reduction) experiments were recorded with the aim to identify the different Co phases present. Co3O4 and LaCoO3 were formed for La loading of 1%, whereas at higher La loading (9%) LaCoO3 and La2O3 oxide prevailed. In both catalysts LaAlO3 phase was also detected. As observed by BET and SEM characterizations, the morphology of the two catalysts was somewhat affected by La:Co atomic ratio and differed dramatically from those of the reference bulk oxides, Co3O4 and the mixed phase LaCoO3/La2O3. Activity tests in C3H6 and CH4 combustion were carried out in order to discriminate the catalytic properties of different phases formed (Co3O4, LaCoO3, La2O3, LaAlO3).