Effects of Diesel Oxidation Catalyst on Nanostructure and Reactivity of Diesel Soot

摘要

In order to investigate the nanostructure changes of diesel soot during the oxidation process, two different types of diesel soot were collected, and their nanostructures were studied on the basis of thermogravimetric analysis and high-resolution transmission electron microscopy analysis. This work shows that the nanostructure alone does not dictate the reactivity of diesel soot, but rather, the oxidation mechanism has a strong effect on the oxidative reactivity. Soot emitted directly from the engine is oxidized under the surface burning mode, which makes the soot retain the typical core-shell structure. However, the diesel oxidation catalyst (DOC) has an influence on the oxidation mechanism of diesel soot as well as the evolution of nanostructure during the oxidation process. Soot sampled after DOC mainly undergoes an internal burning oxidation process that makes the oxidation more rapid, leading to a hollow capsule-like structure during the early stage of oxidation. However, soot becomes less reactive due to the surface burning mode and the more closed outer shell built by the rearrangement of carbon lamellae during the later stage of oxidation.