PGM-free CuO/LaCoO3 nanocomposites: New opportunities for TWC application

Abstract

In this contribution several LaCoO3 based nanocomposites have been prepared and tested for application as Three-Way Catalytic Converters (TWC): the aim is in developing Platinum Group Metal (PGM)-free catalysts. To reach this objective we designed and realized nanocomposites in which active CuO nanoparticles are deposited on active LaCoO3. This perovskite is active in oxidation while copper is active in reduction: catalytic bifunctionality is thus built-in via a tailor-made and controlled nanocomposition. The deposition was carried out by means of an innovative Ammonium-Driving-Deposition precipitation (ADP) procedure allowing to obtain nanocomposites in which CuO is highly dispersed on LaCoO3. This increases the reducibility of the nanocomposites, as revealed by the TPR measurements. The deposition of copper does not alter significantly the surface composition which remains rich in lanthanum oxide/hydroxide, the main effect consisting in a slight increment of surface hydroxylation. Moreover, the copper amount on the LaCoO3 surface does not increase linearly with the nominal composition.Both model reactions (CO oxidation and CO assisted NO reduction) and tests with a synthetic automotive exhaust mixture, including 10 % steam, were carried out. Activity before and after high-temperature aging in steam was also evaluated. We compared the obtained results with the ones of CuO/nickelates of a previous work, to highlight the functionalities gained.In simple CO + NO and CO + O2 mixtures, the deposition of copper oxide on LaCoO3 greatly increases the activity of the nanocomposites in NO reduction (100 % conversion at 350 °C) without significantly affecting the reactivity in CO oxidation. Results with the synthetic automotive exhaust mixture show that Cu loading on ADP-prepared catalysts can significantly improve the NO reduction activity of LaCoO3. Still, NO reduction remains more relevant in O2-poor mixtures (about 100 % conversion around 400 °C in the 10 wt.% Cu loaded), even slightly below the stoichiometric. Some deactivation on hydrocarbon oxidations occurs at low temperatures due to thermal aging, apparently due to coking and surface Cu depletion. Compared to CuO deposited by ADP on LaNiO3 of our earlier studies, cobaltites gain in oxidation activity, but NO reduction remains easier on nickelates. However, the promising performance and the absence of noble critical metals are promising features to develop PGM-free catalysts for the automotive industry.