Monitoring intermediate species formation by DRIFT during the simultaneous removal of soot and NOx over LaAgMnO3 catalyst

Abstract 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.