Ageing and SO2 resistance of Pd containing perovskite-type oxides

The La0.91Mn0.85Ce0.24Pd0.05Oz and La1.034Mn0.966Pd0.05Oz perovskite-type oxides were prepared via a combination of the sol–gel and the combustion synthesis methods. They were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive X-ray, high resolution transmission electron microscopy and electron energy loss spectroscopy. The effect of ageing and SO2 on the catalytic effectiveness of the Pd/perovskite and of a Pd-based commercial three-way catalyst for stoichiometrically operating natural gas fuelled vehicles were investigated. The La1.034Mn0.966Pd0.05Oz catalyst exhibited the highest thermal stability and, in contrast to the La0.91Mn0.85Ce0.24Pd0.05Oz and the commercial catalyst, it appeared significantly activated in the presence of 8 ppm SO2 in the reactant mixture. The formation of La–Pd mixed oxides or/and La2(Mn–Pd)O6, the enhanced surface Pd2+ composition and the low surface sulfur content were suggested as the possible reasons for the activation under sulfur environment.