[Effect of precious metal loaded on LaMnO3 on catalytic oxidation of soot]

Perovskite-type LaMnO3 catalysts were prepared by co-precipitation, and a series of precious metal-coating LaMnO3 catalysts were obtained by impregnation. The activity of catalysts on soot was tested by temperature-programmed reaction. Catalysts were characterized by techniques such as H2-TPR, BET, XRD, SEM and FT-IR. The activity of Pd/LaMnO3 coating 0.5% (weight) Pd is the optimal, and the maximum combustion rate temperature decreases about 40 degrees C , as compared with LaMnO3. When the coating amount is more or less than 0.5%, the ignition temperature is higher than that of pure LaMnO3. The activity of Pd/LaMnO3 is the highest among 5 precious metals-loading catalysts, and the sequence is Au,Ru,Pt and Rh. TPR experiments indicate precious metal can help the transformation of Mn4+ to Mn3+, but has less influence on reduction of Mn3+ to Mn2+ of LaMnO3. The downshift of diffraction angle of XRD indicates some precious metals enter crystal lattice of LaMnO3, the crystal sizes of catalysts become larger after precious metal loading; BET and SEM results show sintering happened to catalysts after catalytic reaction. No obvious changes occur in the IR spectra of catalysts between after and before reaction, indicating catalysts have good structural stability. In conclusion, proper amount precious metal coating on LaMnO3 effectively improve the catalytic activity of LaMnO3 on soot.