The investigation of mechanisms in environmental catalysis using time-resolved methods.

摘要

The formation of nitrogen oxides(NO_x) durign a combustion process is difficult to avoid because of the large exotherm and the consequent problem of avoiding local high-temperature spikes.Consequently,for many applications,such as for automotive power mechanisms of the key catalytic reactions in environmental catalysis can provide an insight into the action of the catalyst,and time-resolved methods offer a powerful means to dtudy these processes under realistic conditions.The use of Temporal Analysis of Products(TAP) and Steady State Isotopic Transient Kinetic Analysis (SSITKa) methods to investigate the reduction of NO_x under various experimental conditions is described.From a detailed analysis of the SSITKA profiles,it is shown that at low temperatures the mechanism for the formation of N_2 and N_2O from NO may differ from the the conventional high-temperature the reaction of N(ads) and NO(ads) may be too high to allow this process to occur at low temperatures.The alternative reaction of NO(ads)+NO(ads)=N_2O(g)+O(ads) is shown to be much more favorable and is consistent with the SSITKA analysis.The remarkable effect of hydrogen as a reductant at low temperatures is described,and alternative interpretations of the role of hydrogen are discussed.