Catalytic oxidation of diesel soot particulates over Ag/LaCoO3 perovskite oxides in air and NOx

Ag/LaCoO3 perovskite catalysts for soot combustion were prepared by the impregnation method. The structure and physicochemical properties of the catalysts were characterized using X-ray diffraction, N2 adsorption-desorption, H2 temperature-programmed reduction, soot temperature- programmed reduction, and X-ray photoelectron spectroscopy. The catalytic activity of the catalysts for soot oxidation was tested by temperature-programmed oxidation in air and in a NOx atmosphere. Metallic Ag particles were the main Ag species. Part of the Ag migrated from the surface to the lattice of the LaCoO3 perovskite, to form La1-xAgxCoO3. This increased the amount of oxygen vacancies in the perovskite structure during thermal treatment. Compared with unmodified LaCoO3, the maximum soot oxidation rate temperature (Tp) decreased by 50–70 °C in air when LaCoO3 was partially modified by Ag, depending on the thermal treatment temperature. The Tp of the Ag/LaCoO3 catalyst calcined at 400 °C in a NOx atmosphere decreased to about 140 °C, compared with that of LaCoO3. Ag particles and oxygen vacancies in the catalysts contributed to their high catalytic activity for soot oxidation. The stable catalytic activity of the Ag/LaCoO3 catalyst calcined at 700 °C in a NOx atmosphere was related to its stable structure.

Graphical AbstractAg migrated into lattice of LaCoO3 perovskite to increase oxygen vacancy in the thermal treatment process. Ag/LaCoO3 catalysts showed high catalytic activity for soot combustion in air and in NOx.Figure optionsDownload as PowerPoint slide