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 degrees C and NO reduction activity was examined at 400 degrees C by an NO-pulse technique. The catalyst weight-loss in reduction was attributed to oxygen release, leading to the formation of metallic Pd-0. About 40% of Pd3+ in LaFe0.95Pd0.05O3 was converted into Pd-0 at 200 degrees C and about 90% at 400 degrees 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 Pd-0 species segregated from LaFe0.95Pd0.05O3 perovskite. The Pd-0 species segregated from LaFePdOx by reduction was assessed to be metallic Pd-0 particles with diameters smaller than 2 nm. Highly dispersed Pd-0 particles on the LaFePdOx catalyst were found to act as breathing active sites that combined high catalytic activity with OSC/ORC performance. (c) 2005 Elsevier B.V. All rights reserved.