Largely Cu-doped LaCo1-xCuxO3 perovskites for TWC: Toward new PGM-free catalysts

Doping of LaCoO3 with copper to add reduction functionality in addition to the known oxidation properties has been investigated, aiming at three-way catalysis (TWC) applications. Nanoscale perovskites with nominal composition LaCo1-xCuxO3, (x=0, 0.1, 0.3, and 0.5) have been synthesized by means of the citrate method. A stable perovskitic phase with rhombohedral geometry up to an unprecedented x=0.5 has been obtained and characterized by BET, X-ray diffraction (XRD), Temperature Programmed Reduction (TPR), X-ray Photoelectron Spectroscopy (XPS), and Scanning Electron Microscopy (SEM). The crystallite size decreases with increasing the copper amount and also the morphology differs; moreover the surface reactivity with respect to atmospheric moisture and carbon dioxide is more evident in the sample with x=0.5. Reactivity has been measured in simple NO+CO and CO+O2 model reactions, as well as with complex mixtures approaching automotive exhaust composition, at both stoichiometric and O2 limiting conditions. The catalysts have been characterized after reaction as well. The perovskite with the highest Cu amount, LaCo0.5Cu0.5O3, exhibits an interesting compromise of oxidation and NO reduction functionality at interesting, low temperatures with very short contact time (GHSV=1,000,000h^-1). Still, activity for NO reduction in real mixtures requires substoichiometric O2.