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

Doping of LaCoO<inf>3</inf> 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 LaCo<inf>1-x</inf>Cu<inf>x</inf>O<inf>3</inf>, (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+O<inf>2</inf> model reactions, as well as with complex mixtures approaching automotive exhaust composition, at both stoichiometric and O<inf>2</inf> limiting conditions. The catalysts have been characterized after reaction as well. The perovskite with the highest Cu amount, LaCo<inf>0.5</inf>Cu<inf>0.5</inf>O<inf>3</inf>, 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 O<inf>2</inf>.