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

The microwave-synthesized-LaAgMnO3-catalyst can eliminate soot and NOx simultaneously below 400 degrees 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, O-2, and NO/O-2 atmospheres was performed. The DRIFTS results indicated that over 200 degrees 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 degrees 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.