The structures, adsorption characteristics of La-Rb-Cu-O perovskite-like complex oxides, and their catalytic performances for the simultaneous removal of nitrogen oxides and diesel soot

The nanometric La2-xRbxCuO4-lambda (A stands for nonstoichiometric oxygen content) perovskite-like complex oxide catalysts were prepared by the sol-gel autocombustion method. Their structures and physicochemical properties were examined by chemical analysis, XRD, SEM, EDS, FT-IR, H-2-TPR, and MS-NO-TPD, and the catalytic performances for the simultaneous removal of nitrogen oxides and diesel soot particulates were investigated by using temperature-programmed oxidation reactions. XRD and IR results demonstrate that the structures of La2-xRbxCuO4-lambda change with the increase in the x value. La2CuO4 possessed a single phase with orthorhombic structure, but the so-called T* phase was formed as x > 0.3 in addition to the orthorhombic phase. A new Cu=O bond was determined by IR vibration band at 980 cm(-1) in the CuO5 of the T* phase. Moreover, the formation of the oxygen vacancy and Cu3+ are also related to the x value, and the oxygen vacancy has an important effect on the catalytic activity for the simultaneous removal of nitrogen oxides and diesel soot particulates because the oxygen vacancy is beneficial to enhancing the adsorption and activation of NO or molecular oxygen. The results of in situ diffuse reflection infrared Fourier transformed (DRIFT) spectra and MS-NO-TPD also demonstrate that there is a close correlation between the adsorption amounts of NO and the oxygen vacancy concentrations of catalysts. For soot combustion, the direct evidence for NO2 indirect catalysis function is found by means of mass spectroscopic measurements. Combining both roles of nanometer effect and NO2 formation, the contact is still very good between catalyst and soot even under loose contact conditions. On the other hand, for NO reduction, the formation of nitrate intermediate species has been identified by in situ DRIFT spectra. These surface nitrate species exist as monodentate, bidentate, and chelating bidentate states and then are reduced by soot to yield N-2- On the basis of the experimental results of NO adsorption, the defective structures of catalysts and NO2 indirect catalysis, a new reaction mechanism is proposed, which can preferably explain the reaction process of the simultaneous removal of NOx and soot over La2-xRbxCuO4-lambda perovskite-like complex oxides.