Plasma catalysis with perovskite-type catalysts for the removal of NO and CH4 from combustion exhausts

The removal of NO and CH4 from quaternary gas mixtures simulating the conditions existing in real combustion exhausts has been studied with a hybrid system integrating plasma activation and a La1−xSrxCoO3−d perovskite-type catalyst. The plasma reaction produces the conversion of NO into N2 plus O2 and the oxidation of CH4 into CO + H2O. Incorporation of the catalyst favors the oxidation of CH4 into CO2 at 190 °C. At this temperature, no oxidation of CO or CH4 is found in a conventional catalytic reactor. A similar plasma + catalyst experiment with SiO2 found much lower CO2 production, indicating that the perovskite is actively involved in the oxidation of CO. The efficiency of NO removal decreased with the amount of perovskite, although this efficiency could be restored by adding carbon to the reactor. Experiments using optical emission spectroscopy (OES) and in situ X-ray photoemission spectroscopy (XPS) were carried out to gain insight into the synergetic effects found with the catalyst. OES intermediate species, including NH∗, CN∗, CO∗, and CH∗, were found in the plasma. XPS experiments of samples exposed to plasmas showed the formation of NOx and CN species, indicating the active involvement of the catalyst in the reaction.