Reducibility of Co3+ in perovskite-type LaCoO3 and promotion of copper on the reduction of Co3+ in perovskite-type oxides

The reducibility of Co3+ in LaCoO3 and the promotion of copper on the reduction of Co3+ in perovskite-type oxides have been studied by temperature programmed reduction (TPR), temperature programmed oxidation (TPO), X-ray diffraction (XRD) and infrared spectroscopy (IR). Quantitative TPR and TPO analyses propose that the reduction of Co3+ in LaCoO3 to Co0 belongs to a one-step process and that every TPR peak represents the reduction of every Co3+ species to Co0 in the crystallite structure. Accordingly, the produced Co0 is assumed to be atomically located in the perovskite lattice provided the perovskite structure is retained after reduction. Quantitative TPR analyses also indicates that copper located in LaCo0.85Cu0.15O3 promotes regularly the reduction of various Co3+ species whereas copper doped on LaCoO3 does irregularly. The action of the latter leads to more efficient reduction of Co3+ to atomically dispersed Co0 over a useful temperature range for catalytic purposes. TPR, XRD and IR studies show that the perovskite structure of LaCo0.85Cu0.15O3 is somewhat less stable than that of LaCoO3 and that the perovskite structural stability of LaCoO3 is not weakened by the doping of copper.