Kinetics of catalyzed and non-catalyzed soot oxidation with nitrogen dioxide under regeneration particle trap conditions

BACKGROUND: For compliance with the regulations on diesel particulate matter, car manufacturers have developed diesel particulate filters (DPF). These technologies require a regeneration method which oxidizes soot deposits in the filter. In diesel exhaust emissions there are two suitable oxidizing gases: oxygen and nitrogen dioxide. Nitrogen dioxide is much more active than O-2 and can directly attack the carbon surface. This work describes the kinetics of the oxidation of soot by NO2 over a wide range of conditions relevant for DPF. RESULTS: The catalyzed and the non-catalyzed oxidation of soot have been performed in a fixed-bed reactor. The experimental results show that the overall oxidation process can be described by two additive parallel reactions: a direct C-NO2 reaction catalyzed by H2O and a cooperative C-NO2-O-2 reaction catalyzed by the Pt/Al2O3 catalyst. The results obtained allow to propose the following kinetic law for the specific rates of the catalyzed and the non-catalyzed oxidation of soot in the regeneration filter conditions: r (s(-1)) = 0.48 exp (-26700/RT) X-NO2(0.6) + 1395 (-47800/RT) XNO2XO20.3 r(cat) (s(-1)) = 0.51 exp (-26800/RT) X-NO2(0.6) + 51.4 exp (-52200/RT) (XNO2XO20.3)-X-0.4 CONCLUSION: The kinetic parameters describing the oxidation rate of soot by NO2 over a range of temperature and gas composition have been obtained. The extracted kinetics data are relevant for modeling the removal of trapping soot in automotive gas exhaust technology. (C) 2009 Society of Chemical Industry