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

Abstract

In order to elucidate the activity of LaFePdO x -based automobile three-way catalysts at low-temperatures, the oxygen release capacity (ORC) and oxygen storage capacity (OSC) of LaFePdO x 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 Pd 0. About 40% of Pd 3+ in LaFe 0.95Pd 0.05O 3 was converted into Pd 0 at 200 °C and about 90% at 400 °C. ORC and OSC as observed for the LaFePdO x 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 LaFePdO x catalysts can probably be attributed to the very fine dispersion of Pd 0 species segregated from LaFe 0.95Pd 0.05O 3 perovskite. The Pd 0 species segregated from LaFePdO x by reduction was assessed to be metallic Pd 0 particles with diameters smaller than 2 nm. Highly dispersed Pd 0 particles on the LaFePdO x catalyst were found to act as “breathing active sites” that combined high catalytic activity with OSC/ORC performance.