Detailed Kinetic Analysis of Soot Oxidation by NO₂, NO, and NO + O₂

Abstract

Kinetic parameters for soot oxidation by O2 and NOx are estimated by fitting for product selectivity and global rates. Depending on the gas mixture, the competition of two surface reactions for lumped C*(NO) complexes determines whether N2 or NO2 and CO2 are produced. NO adsorption and soot conversion are much improved when O2 is added to NO because the presence of oxygen on soot favors the competing step of reaction with C*(NO). For NO, the adsorption/desorption steps are rate determining; the importance of CO and CO2 formation steps grows with increasing O2 concentration. For soot + NO2, adsorption/desorption of NO2 controls the rate above 600 °C; below this temperature, it is the surface formation of C*(ONO2). Experiments with soot and graphite show that differences in BET area are not sufficient to model tendencies in NO chemisorption and CO and CO2 formation.