Reaction mechanism for NO oxidation on the soot surface using a quantum chemistry

Abstract

Compared with the gas phase oxidation of NO, the NO surface oxidation on soot is more effective, which is critical to keep efficient diesel particulate filter regeneration and high selective catalytic reduction conversion rates. To fill the knowledge gaps in catalytic oxidation of NO on the soot surface, it is integral to study the detailed mechanism in the NO-O2-soot reaction. This paper explores soot surface catalytic role in changing NO into NO2 using density functional theory and chemical kinetic analysis. The results exhibit that the adsorption stability of NO on the soot sites is higher than that of O2. The adsorbed NO interacts with O2 on the soot surface, which reduces the activation energy of C(O2) decomposition. The NO by N-down adsorption is oxidized readily by O2 with an energy barrier of 10.9 kJ/mol, and the reaction rate is 8.8 × 1011 s−1 at 300 K. The formation of NO2 depends mainly on C(NO2) and C(ONO2) decomposition during surface oxidation. The NO cleavage will produce C(O) and C(N), which is difficult to be further oxidized by O2 or NO. This study reveals the mechanism for soot surface catalytic of NO oxidation, which explains the results of previous experiments for the NO-O2-soot reaction system.