Simultaneous removal of NOx and diesel soot over nanometer Ln-Na-Cu-O perovskite-like complex oxide catalysts

The nanometric Ln-Na-Cu-O (Ln = La, Pr, Nd, Sm, Gd) perovskite-like complex oxide catalysts were prepared by sol–gel auto-combustion method using citric acid as a ligand and an adjusting agent of particle-size and morphology. Their structures and physico-chemical properties were examined by chemical analysis, XRD, SEM, FT-IR, H2-TPR and MS-NO-TPD. The catalytic performances of these perovskite-like oxides for the simultaneous removal of soot and NOx were investigated by a technique of the temperature-programmed reaction (TPR). In the Ln-Na-Cu-O catalysts, the partial substitution of Na for La at A-site led to the formation of Cu3+ and/or oxygen vacancy, thus the catalytic activity was remarkably enhanced. The optimal substitution amount of Na (x) is equal to 0.3 for the reduction of NOx, and x is equal to 0.7 for soot combustion. Moreover, attributing to the effects of very small surface particle sizes of the catalysts and the strong oxidizing ability of NO2 which was produced from NO and O2 in the reactant gases on these catalysts, the nanometric Ln-Na-Cu-O perovskite-like oxides exhibit very high catalytic activities for soot combustion even under loose contact conditions between soot and the catalyst.