Oxidation evolutions of soot surface and pore properties with different O2-NO2 mixtures and temperatures

Abstract

Soot oxidation evolutions at various oxidation degrees under different O2-NO2 mixtures and temperatures were performed. Results indicated that the internal burning-out process represented by shell-like particles at 500 °C independent on NO2 concentration, while the development of hollow shells for the soot was suppressed with increasing the temperature. A tendency with soot toward a less ordered arrangement with short and defective graphene layers after oxidizing at 500 °C was also observed, which was suppressed with added NO2 and increasing temperature. Many carbon oxygen functionalities produced at 40% oxidation and the intensity of the peak gradually increased as the increase of the oxidation degree, while the increase of the peak intensity became less sensitive with added NO2 and increasing temperature. Abundant micropores and mesopores formed inside the particles during the soot oxidation process depending on oxidizer and temperature, micropores (smaller than 2 nm) were extensively generated at the early stages of the oxidation while mesopores increased sharply after 20% oxidation. The trends were correspondent to the oxidation modes with different oxidizer and temperature. The correlationship observation suggested that soot oxidation behavior was dependent on competing rates of reaction kinetics versus mass transport of oxidizer according to the oxidation evolution of surface and pore.