A series of CeαMn1-αO2 catalysts supported on g-alumina with various molar concentrations of Ce (α, from 0 to 0.90) was synthesized by coprecipitation, applying two different precipitating agents, namely, sodium hydroxide (method 1) and sodium carbonate (method 2), with the use of sodium permanganate as a redox agent for precipitation. XRD profiles of the supported samples revealed the predominant abundance of a typical fluorite crystalline structure. TPR thermograms of supported samples were displaced towards lower temperatures with increasing Mn concentration, in contrast with the bulk samples. The supported Ce-Mn samples exhibited a greater performance in n-hexane elimination than did the corresponding simple oxides. The sample Ce0.33Mn0.67O2 obtained by method 2 presented the best activity, probably due to the enrichment of Ce4+, Mn3+ and Mn4+ surface species, an excess of superfi...

Catalysts based on Ni-Fe-a with a catalyst ratio of a = Ni/(Ni + Fe) (a = 0.8 and 0.9) supported on γ-Al2O3 were prepared by coprecipitation-deposition and tested for the oxidative dehydrogenation (ODH) of ethane. The bulk mixed samples exhibited 30% greater selectivity toward ethylene than did the corresponding simple oxide NiO. Meanwhile, the most selective sample, NiFe-0.9/γ-Al2O3, achieved a maximum of 94% at 400 °C. The remarkable selectivity of NiFe-0.9/γ-Al2O3 was attributed to the partial substitution effect of Ni2+ by Fe3+, thus allowing those catalysts to form oxygen sites that are specific for the partial oxidation of ethane to ethylene. Some additional factors that could have contributed to ethylene selectivity were the formation of low-reducibility species with controlled particle size, a better dispersion of the active phase over the support and the synergy of Fe3+ with...