Characterization of Catalyzed Soot Oxidation with NO2, NO and O2 using a Lab-Scale Flow Reactor System

Today's diesel PM reduction systems are mainly based on catalyzed particulate filter(CPF) systems. However, most of their reaction kinetics remain unresolved. Among others, the soot oxidation rate over catalyst is particularly important in the evaluation of the performance of the catalysts and the efficient control of CPF regeneration. This study, therefore, investigated the oxidation rate of carbon black (Printex-U) over various Pt supported catalysts using a flow reactor setup simulating diesel exhaust conditions. Compared to non-catalyzed soot oxidation, the oxidation rate of carbon black over Pt catalysts was to an extent shifted towards low temperatures. This activity enhancement of soot oxidation over a catalyst can be attributed principally to NO to NO₂ conversion because NO₂ oxidizes soot with much lower activation energy (Ea=60kJ/mol) than O₂ (Ea=177kJ/mol). Moreover, the oxidation rate of carbon black and catalyst mixture may be accelerated because NO to NO₂ conversion takes place on multiple occasions while the NO molecule passes through the sample bed. In addition, the order of reactivity of Pt catalysts was Pt/CeO₂ > Pt/SiO₂ > Pt/Al₂O₃ in the tested temperature range up to 600°C. For the Pt/CeO₂ catalyst, the oxidation rate was about three times greater than that of non-catalyzed carbon black with NO₂ at 500 °C.