Isotopic study of the La0.7Ag0.3MnOδ≤3 perovskite-catalyzed soot oxidation in presence of NO

Abstract

Soot oxidation process over La0.7Ag0.3MnOδ≤3 (LAM) and LaMnO3 (LM) catalysts was studied through 18O2 isotopic labelling experiments in the presence and absence of NO, using catalyst-soot mixtures under loose contact conditions. Isotopic exchange experiments evidenced that silver-particles enhanced oxygen exchange capacity, explained by the increase of oxygen active sites formed due to the charge compensation mechanism in the perovskite-like structure due to silver incorporation, and metallic-silver-segregated on catalytic surface. This enhanced oxygen exchange ability leads to the improvement of the catalytic soot oxidation capacity. The elucidated reaction-pathway indicated that catalyst oxygen is transferred to soot, and then gas-phase-oxygen occupies the vacancies created. Furthermore, 16-oxygen species coming from catalyst play an important role in the formation of NOx-adsorbed species that lead to NO2 formation, which assists soot oxidation. The desorption of NO2 was favored with Ag-particles presence because it promoted the formation of less thermally stable adsorbed NOx species.