Display omitted •O-vacancies and Ag(s) over La0.7Ag0.3MnO3 are the most active sites for NO and oxygen adsorption.•Chelating and bridging nitrates along with Ag-nitrites are the primary reaction intermediates for the NO oxidation.•Monodentate nitrates and Ag-nitrates were considered NOx storage species over 400 °C.•A reaction pathway for soot and NO removal over La0.7Ag0.3MnO3 was proposed based on DRIFT results.•The silver-free catalyst was less active than its counterpart due to changes in nitrogenous species distribution. The microwave-synthesized-LaAgMnO3-catalyst can eliminate soot and NOx simultaneously below 400 °C. To get some insight about the chemical species formed on catalyst and soot surfaces, in situ diffuse reflectanced infrared Fourier transform (DRIFT) spectroscopy under NO, O2, and NO/O2 atmospheres was performed. The DRIFTS results indicated that over 200 °C, at least four types of nitrate-species, mono- and bi-dentate nitrates (bridging and chelating) on the perovskite, as well as Ag-nitrite/nitrate, with different thermos-stabilities were formed. The decomposition of less stable surface nitrates/nitrites accounts for NO2 formation which assisted soot oxidation. The transformation-decomposition of nitrite/nitrate compounds coincided with the appearance of CO2 and carbonate-species coming from re-adsorption of soot combustion products. Monodentate nitrates, which are more stable nitrate-species, were considered NOx storage-species over 400 °C. Chelating- and bi-dentate nitrates formed on perovskite oxygen vacancies appear to be the primary reaction intermediates for the NO oxidation reaction over the Ag-doped perovskite catalyst.