Catalytic reduction of NO by propene over LaCo1−xCuxO3 perovskites synthesized by reactive grinding
One series of LaCo1−xCuxO3 perovskites with high specific surface area was prepared by the new method designated as reactive grinding. These solids were characterized by N2 adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), H2-temperature programmed reduction (TPR), O2-temperature programmed desorption (TPD), NO + O2-TPD, C3H6-TPD, NO + O2-temperature programmed surface reaction (TPSR) under C3H6/He flow as well as catalytic reduction of NO activity tests. The catalytic performance of unsubstituted sample is poor with a maximum conversion to N2 of 19% at 500 °C at a space velocity of 55,000 h−1 (3000 ppm NO, 3000 ppm C3H6, 1% O2 in helium) but it is improved by incorporation of Cu into the lattice. A maximal N2 yield of 46% was observed over LaCo0.8Cu0.2O3 under the same conditions. Not only the abundance of α-oxygen but also the mobility of β-oxygen of lanthanum cobaltite was remarkably enhanced by Cu substitution according to O2-TPD and H2-TPR studies. The better performance of Cu-substituted samples is likely to correspond to the essential nature of Cu and facility to form nitrate species in NO transformation conditions. In the absence of O2, the reduction of NO by C3H6 was performed over LaCo0.8Cu0.2O3, leading to a maximal conversion to N2 of 73% accompanied with the appearance of some organo nitrogen compounds (identified as mainly C3H7NO2). Subsequently, a mechanism involving the formation of an organic nitro intermediate, which further converts into N2, CO2 and H2O via isocyanate, was proposed. Gaseous oxygen acts rather as an inhibitor in the reaction of NO and C3H6 over highly oxidative LaCo0.8Cu0.2O3 due to the heavily unselective combustion of C3H6 by O2.
Journal: Applied Catalysis B: Environmental - Volume 64, Issues 3–4, 2 May 2006, Pages 220–233