Calcium and Copper Substitution in Stoichiometric and La-deficient LaFeO3 Compositions: A Starting Point in Next Generation of Three-Way-Catalysts for Gasoline Engines

Calcium and copper substitutions, in A-site and B-site respectively, of parent stoichiometric LaFeO3 and La-deficient La0.7FeO3 perovskites led to significant improvements in the kinetics of CO and propene oxidation in typical three-way operating conditions. La-deficient La0.7Fe1-yCuyO3 perovskites were found more prone to surface copper oxide segregation leading to more active extra-framework copper oxide species in CO oxidation. Optimal performances were obtained on La0.7Fe0.8Cu0.2O3 composition. At higher Cu content, strong copper agglomeration leads to deactivation. More stable systems were obtained on dual substituted samples thanks to calcium substitution stabilizing copper inside the perovskite lattice and slowing down subsequent surface agglomeration. Rate enhancements in propene oxidation is observed on A-site deficient La0.6CaxFe0.8Cu0.2O3 with x <= 0.2 but a sharp loss in rate is observed on stoichiometric La0.6Ca0.4Fe0.8Cu0.2O3 perovskite explained by a progressive shift from suprafacial to intrafacial mechanism involving in this latter case the redox Fe4+/Fe3+ couple and lattice oxygen species.