Influence of synthesis conditions on NO oxidation and NO_x storage performances of La_0.7Sr_0.3MnO₃ perovskite-type catalyst in lean-burn atmospheres

Synthesis conditions of catalysts can significantly affect catalytic activities for a certain reaction. Here, a series of the La_0.7Sr _0.3MnO₃ perovskite-type catalysts was prepared by the sol-gel method under the different synthesis conditions. The faster calefactive velocities during calcination of the xerogel precursors would produce a lot of the impurities and cause the dropped amount of the excessive oxygen in perovskite, as well as the aggregated particles and the decreased surface areas; the higher calcination temperature would sinter the perovskite phases seriously; and the initial pH value of the precursor solution would greatly affect the morphology of the catalysts including the shape and the size, which directly linked to their NO_x storage capacity. Moreover, our findings revealed that the NO oxidation ability was determined by the amount of the excessive oxygen species in the perovskite. Here, the optimum synthesis conditions were achieved with the calcination temperature of 700 C, the calefactive velocity of 2 C min^-1, and the precursor solution of pH = 8. This catalyst presented the best performances for the NO oxidization and NO_x storage, i.e. the NO-to-NO₂ conversion of 70.2% and the NO_x storage capacity of 170.4 μmol g^-1.