Substituted La1-xCe xCoO3 perovskite-type oxides (0.0≤x≤0.9), prepared by the self-combustion method, have been investigated as catalysts in soot combustion. The characterization results indicate modification in the specific surface area, crystal structure, oxygen mobility and reducibility of cobaltite upon cerium substitution. Cobaltite structure does not tolerate more than 50% substitution of La by Ce. For higher Ce substitution the perovskite structure is lost and mixed oxides are detected. Further destruction of the perovskite structure in a reductive process indicates a lower catalytic role of the perovskite structure in the catalytic combustion of soot regarding to the chemical composition of the La1-xCe xCoO3 system. After the reductive process, only a slight increase in the catalytic activity of the samples with low Ce content (x≤0.3) while a larger increased was detected for those with larger amount of Ce(x≥0.5). These results suggest that the activity of these materials for soot combustion is improved by two factors: i) the increasing of CeO2 content, closely related to higher material capacity for oxygen transfer from catalyst to carbonaceous surface and ii) the formation of larger CeO2 crystals in the higher-Ce-content samples after H2 reduction, responsible of the improvement of the oxygen exchange and number of contact points between catalyst and soot.

The reaction kinetics of methane combustion over La1-xCa xFeO3 perovskites (x=0.0, 0.2, 0.4) was studied. The results show that the catalytic activity is higher in the calcium-doped perovskites. It is found that this higher catalytic activity is related to a lower activation energy. The value of the activation energy is not affected by the level of Ca-doping. The observed difference in the catalytic activity between the doped perovskites is interpreted as a consequence of the so-called compensatory effect, i.e., a larger pre-exponential factor which results from the higher number of active sites promoted by defect reactions triggered by the substitution of lanthanum by calcium. The substitution of lanthanum by a lower valence cation, as calcium, entails both the formation of oxygen vacancies and oxidation of some iron ions from Fe3+ to Fe4+, in order to preserve the electroneutrality. The oxygen vacancies account for the increasing participation of lattice oxygen in the combustion kinetics as the calcium doping increases. The experimental results were satisfactorily fitted to the Rideal-Elay mechanism.

O potencial elétrico de uma membrana dopada com trioleína e colocada entre duas soluções aquosas de cloretos de sódio e potássio foi analisada para verificar a ocorrência de caos determinístico, usando métodos padrão de teoria de sistemas dinâmicos não lineares. Os resultados fornecem evidências sólidas de que este sistema apresenta dinâmica caótica, e não é apenas um exemplo de ruído experimental.

The electric potential of a membrane doped with triolein, placed between aqueous solutions of sodium chloride and potassium chloride, was analyzed for the existence of deterministic chaos using standard methods of nonlinear dynamics system theory. The results provide solid evidence that the system shows a chaotic dynamics and not just an example of experimental noise in the data.