The formation mechanism of N2O and NH3 on PtRh three-way catalyst of natural gas vehicles

The mechanism of the NO conversion to poisonous substrates, such as NH3 and N2O on a model Pt/CeO2+Rh/LA three-way catalyst (TWC) during the treatment of exhaust emission from natural gas vehicles (NGVs) was investigated. The in situ DRIFTS results showed that the main pathway of NO reduction is the reaction of nitrite/nitrate species formed by NO adsorbed on CeO2 with CH4. It was further elucidated by O1s and DRIFTS that the formation of N2O at low temperature is ascribed to competitive reactions of cyanide (-CN) species with O2 and NOx. Specifically, for Pt/Ce catalysts, N2 and CO2 are formed due to the preferential reaction of -CN species with the surface adsorbed oxygen (Oads) species on the catalyst. While for Pt/Ce-Rh/LA550 and Pt/Ce-Rh/LA600 catalysts, N2O is formed due to the easier reaction of -CN with NOx. At high temperature, the catalyst mechanically mixed with Rh/LAx increased the concentration of Oads, which promoted CH4 oxidation and inhibited the reaction of NO with C-containing compounds to isocyanate (NCO*), thus reducing NH3 formation. Our work may provide new ideas for developing advanced TWC for NGVs with lower emission of NH3 and N2O.