Detailed experimental investigation of the NOx reaction pathways of three-way catalysts with focus on intermediate reactions of NH3 and N2O

Abstract

In this work possible reaction pathways of NOx were investigated for a three-way catalyst on a synthetic gas test bench with a focus on intermediately produced NH3 and N2O. NH3 formation during a typical lean-to-rich transient was verified. Further experiments were carried out in Ar atmosphere allowing to directly determine the N2 selectivity. It could be shown that the catalyst's oxygen storage capacity (OSC), which is implemented by addition of CeO2 to the washcoat material, plays a significant role and that NO can fill the oxygen storage in the absence of O2. Further, no nitrogen species were found to be stored. Also, intermediately produced NH3 was oxidized by stored oxygen with a high selectivity to N2. As soon as the OSC was fully exhausted, NH3 dissociated, leading to the formation of N2 and H2. The presence of side products and secondary emissions strongly depends on the actual operating conditions.