Characterization and catalytic properties of perovskites with nominal compositions La1-xSrxAl1-2yCuyRuyO3

Journal article, 1994

Nine different metal oxide catalysts were prepared by impregnating alumina washcoats with water solutions containing La3+, Sr2+, Cu2+ and Ru3+ ions and calcining them at 900-degrees-C. The produced samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) studies combined with energy-dispersive spectroscopy (EDS) analysis, X-ray powder diffraction and specific surface area measurements. A perovskite phase of the nominal composition La1-xSrxAl1-2yCuRuyO3 was found in all samples, in increasing amount in the samples with increasing contents of strontium and ruthenium. The catalysts were evaluated with respect to light-off temperatures and redox characteristics using two gas mixtures, one containing NO/CO/C3H6/O2/N2 and the other NO/CO/N2. The light-off temperatures for nitric oxide reduction decreased from 534 to 333-degrees-C for the catalysts without and with strontium and ruthenium, respectively. In the presence of oxygen the conversion of nitric oxide declined rapidly under oxidative conditions whereas in absence of oxygen this decline was less pronounced and found to be linear over the entire redox interval studied. These studies suggest that the perovskite phase takes an active part in the conversion of nitric oxide and carbon monoxide to nitrogen and carbon dioxide.