CHARACTERIZATION AND CATALYTIC PROPERTIES OF PEROVSKITES WITH NOMINALCOMPOSITIONS LA1-XSRXAL1-2YCUYRUYO3

Nine different metal oxide catalysts were prepared by impregnating alu mina washcoats with water solutions containing La3+, Sr2+, Cu2+ and Ru 3+ ions and calcining them at 900-degrees-C. The produced samples were characterized by scanning electron microscopy (SEM), transmission ele ctron microscopy (TEM) studies combined with energy-dispersive spectro scopy (EDS) analysis, X-ray powder diffraction and specific surface ar ea measurements. A perovskite phase of the nominal composition La1-xSr xAl1-2yCuRuyO3 was found in all samples, in increasing amount in the s amples with increasing contents of strontium and ruthenium. The cataly sts were evaluated with respect to light-off temperatures and redox ch aracteristics using two gas mixtures, one containing NO/CO/C3H6/O2/N2 and the other NO/CO/N2. The light-off temperatures for nitric oxide re duction decreased from 534 to 333-degrees-C for the catalysts without and with strontium and ruthenium, respectively. In the presence of oxy gen the conversion of nitric oxide declined rapidly under oxidative co nditions 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.