A Steady State Isotopic Transient Kientic Analysis of NO Reduction over Pt/SiO_2 under Lean Burn conditions

摘要

Steady State Isotopic Transient Kinetic Analysis techniques have been used, in conjunction with Mathematical modelling, in an attempt to clarify the mechanism of the NO/C_3H_6/O_2 reaction over supported Pt catalysts. The isotopic switches carried out under steady state reaction involved replacing NO in an NO/O_2/C_2H_6 stream with an equivalent volume and pressure of labelled ~15NO. Profiles of reactants and products after the swithc, along with the profile of an inert tracer gas (Ar), are monitored as a function of time. The profile of an inert tracer gas (Ar), are monitored as a function of tiem. The profiles of the unlabelled products of the reaction, N_2, N_2O and NO_2 yield information about the surface coverages of reactive intermediates on the catalyst surface during the steady state reaction and can be used to analyse the fraction of the surface involved in reaction. The profiles can also be used to estiamte the time constant for the production of the product molecules and thus also gives information abotu the reactivity of the adsorbed species. From the corresponding experimental data the fraction of heavy (~15N) isotope in the products (N_2 and N_2O) was calculated; (alpha (N_2O) can be calcualted in a similar way).