The reducing capability of palladium segregated from perovskite-type LaFePdOx automotive catalysts

In order to elucidate the activity of LaFePdOx-based automobile three-way catalysts at low-temperatures, the oxygen release capacity (ORC) and oxygen storage capacity (OSC) of LaFePdOx were measured by means of thermogravimetry (TG) in a hydrogen-containing atmosphere at 200-400 °C and NO reduction activity was examined at 400 °C by an NO-pulse technique. The catalyst weight-loss in reduction was attributed to oxygen release, leading to the formation of metallic Pd0. About 40% of Pd3+ in LaFe0.95Pd0.05O3 was converted into Pd0 at 200 °C and about 90% at 400 °C. ORC and OSC as observed for the LaFePdOx catalysts were found to be comparable to results seen when adding Ce-based oxides as an OSC material in a commercial catalytic converter. The reducing capability of Pd for NO reduction demonstrated by the reduced LaFePdOx catalysts can probably be attributed to the very fine dispersion of Pd0 species segregated from LaFe0.95Pd0.05O3 perovskite. The Pd0 species segregated from LaFePdOx by reduction was assessed to be metallic Pd0 particles with diameters smaller than 2 nm. Highly dispersed Pd0 particles on the LaFePdOx catalyst were found to act as “breathing active sites” that combined high catalytic activity with OSC/ORC performance.