Effects of H2O and O2 on the Reaction of NO Reduction by CH4 under Stoichiometric Natural Gas Vehicles

Composite support CeZrYLa + LaAl was prepared by co-precipitation, and platinum catalyst supported on the composite support was prepared by impregnation. The behavior of the Pt catalyst for the reaction of NO reduction by CH4 from the exhausts of natural gas vehicles (NGVs) was studied under stoichiometric conditions. Additionally, the effects of 10% (volume fraction, phi) H2O and stoichiometric O-2 on the reaction in the presence of CO2 were also investigated. Results show that N-2 and CO2 were the main products for the different reactions, CO was detected under high temperature, and NO was detected under low temperature (in the presence of O-2, the NO was NO2, whereas the NO was N2O when no O-2 was present). In the presence of 10% (phi) H2O, the conversion of CH4 noticeably decreased and NO conversion remained unchanged, possibly because the presence of H2O weakens the reforming reaction of CH4 with CO2, but does not affect the activity of NO reduction by CH4. In the presence of stoichiometric O-2, there was an obvious increase of CH4 conversion and a decrease of NO conversion. These could be explained by the competition between NO and O-2, where the oxidation of methane by O-2 is the main reaction, limiting the reaction of NO reduction by CH4. Moreover, in the presence of 10% (phi) H2O and stoichiometric O-2, CO2 reforming of CH4 was negligible. Numerous reactions were detected simultaneously, such as the oxidation of CH, by NO, steam reforming of CH4, and the reduction of NO by CH4, thus improving the conversions of CH4 and NO.