Detailed kinetic modeling of the NH3–NO/NO2 SCR reactions over a commercial Cu-zeolite catalyst for Diesel exhausts after treatment

A dynamic micro-kinetic model is developed in close agreement with all the details of the NO2-related SCR catalytic chemistry over a Cu-zeolite catalyst. The rate parameters are estimated from transient kinetic runs, namely isothermal concentration step changes, temperature programmed desorption (TPD) and temperature programmed surface reaction (TPSR) experiments, designed to address the individual steps in the surface mechanism, including adsorption of ammonia, adsorption of NO2 in the form of surface nitrites and nitrates, decomposition of nitrites to nitrogen via reaction with ammonia, reversible reduction of nitrates to nitrites by NO (Fast SCR route), and direct reduction of nitrates by ammonia (NO2-SCR route). The fitted set of rate equations is able to predict the complex transient behaviors associated with the global Fast-SCR and NO2-SCR reactions observed in T-ramp validation experiments.

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► Mechanistic transient kinetic model of NO2-related SCR reactions over Cu-zeolite.
► Nitrite/nitrates storage/reactivity are key to transient kinetic modeling of NO/NO2–NH3-SCR at low-T.
► Nitrates storage/reactivity with NO and NH3 found in close agreement with surface chemistry over Fe-zeolites.
► Results are relevant for modeling of cold-start transients.