Effect of CO2 on the selective catalytic reduction of NOx with NH3 of Fe0.4Ce0.6O2-δ catalyst: adsorption behavior

Abstract

Besides of NOx, CO2 is always abundantly present in the exhaust gas stream, which is important for the investigation of de-NOx. The presence of CO2 has an inhibiting effect on the NH3-SCR activity at temperatures below 300°C for the Fe0.4Ce0.6O2-δ catalysts. To make clear this impact of CO2 for NH3-SCR reaction, we further investigate the changes of NH3 and NOx adsorption behaviors, using in situ TPD and in situ DRIFTS technologies. The DRIFT spectra of CO2 adsorption show that weakly adsorbed carbonate and bicarbonate species were formed, leading to the changes in adsorption and activation behaviors of NH3 and NOx. On the one hand, the formed carbonate and bicarbonate can act as new acid sites thereby improvement of NH3 adsorption. On the other hand, the adsorption of NOx on Fe-O-Ce is suppressed by CO2 results from its competitive adsorption. Especially, the formation path of monodentate nitrate may be blocked by CO2, which is usually active intermediate species for the NH3-SCR reaction, resulting in the deactivation of CO2.