Perovskites as Alternatives to Noble Metals in Automotive Exhaust Abatement: Activation of Oxygen on LaCrO3 and LaMnO3

Abstract

In this contribution, perovskitic materials have been tested as substitutes of noble metals in automotive exhaust abatement devices. LaMnO3 and LaCrO3 were the chosen materials. Samples were characterized by means of X-ray diffraction, scanning electron microscopy, BET surface area, temperature programmed reduction and X-ray photoelectron spectroscopy. Reactions tested have been soot oxidation by 10% O2 and 0.5% NO and stoichiometric 1% NO reduction by 1% CO. LaMnO3 has proved to be a good catalyst for oxidation reactions, whereas LaCrO3 is more suitable for reduction reactions. TPR and XPS analysis have shown a greater oxygen exchange capability in LaMnO3 than in LaCrO3, which is less reducible and strongly bonds adsorbed oxygen. Substitution of 20% La in the A-site of the perovskitic lattice with K has increased activity of both catalysts. In the case of LaCrO3, however, this has lead to a slower reaction course. NO reduction test clearly indicates that Cr-containing perovskite is more suitable for reduction reactions, whereas Mn-based materials are a good choice for oxidative applications. This can relate to superficial oxygen properties and bulk oxygen mobility, as shown by XPS and TPR results.