Transient behaviour of catalytic monolith with NOx storage capacity

Transient behaviour of catalytic monolith converter with NOx storage is studied under conditions typical for automobiles with lean-burn engines (i.e., diesel and advanced gasoline ones). Periodical alternation of inlet concentrations is applied—NOx are adsorbed on the catalyst surface during a long reductant-lean phase (2–3 min) and then reduced to N2 within a short reductant-rich phase (2–6 s). Samples of industrial NOx storage and reduction catalyst of NM/Ba/CeO2/γ-Al2O3 type (NM = noble metal), washcoated on 400 cpsi cordierite substrate, are used in the study. Effects of the rich-phase length and composition on the overall NOx conversions are examined experimentally. Reduction of NOx by CO, H2 and unburned hydrocarbons (represented by C3H6) in the presence of CO2 and H2O is considered. Effective, spatially 1D, heterogeneous mathematical model of catalytic monolith with NOx and oxygen storage capacity is described. The minimum set of experiments needed for the evaluation of relevant reaction kinetic parameters is discussed: (i) CO, H2 and HC oxidation light-off under both lean and rich conditions, including inhibition effects, (ii) NO/NO2 transformation, (iii) NOx storage, including temperature dependence of effective NOx storage capacity, (iv) water gas shift and steam reforming under rich conditions, i.e., in situ production of hydrogen, (v) oxygen storage and reduction, including temperature dependence of effective oxygen storage capacity, and (vi) NOx desorption and reduction under rich conditions. The experimental data are compared with the simulation results.