Investigation of the formation characteristics of N2O and NH3 for stoichiometric natural gas engines with Pd-only catalyst

Abstract

To investigate the effects of inlet temperature and exhaust gas composition on the formation characteristics of nitrous oxide (N2O) and ammonia (NH3) for stoichiometric natural gas engines with Pd-only three-way-catalyst (TWC), a global model of Pd-only TWC by constructing a comprehensive catalytic reaction mechanism was established and a simulation investigation of the effect of inlet temperature, H2O content, oxygen (O2) concentration and methane (CH4) concentration on the formation of N2O and NH3 was conducted. The results showed that the inlet temperature played an important role in the formation of N2O and NH3. N2O was easy to generate N2 through secondary reduction under high temperatures·NH3 was formed by the reduction of nitric oxide (NO) through hydrogen (H2). The H2 required for the reduction came from the reactions of steam reforming and water gas shift on the Pd surface. The formation of NH3 by the reduction of NO through H2 at a temperature above 750 K. Secondly, the maximum N2O concentration and NH3 formation raised with the increase of H2O content. In addition, the emission of N2O and NH3 decreased to zero by controlling the exhaust gas temperature and O2 concentration. Finally, the formation of N2O decreased with the increase of CH4 concentration, which was contrary to NH3. The emission of N2O and NH3 declined to zero by controlling the exhaust gas temperature in the range of 700 K–750 K under 1500 × 10−6 CH4.