Diesel soot combustion in air-NO environment: Evolution of functional groups on soot surfaces

It is inevitable for NO to be involved in the soot combustion in diesel particulate filters (DPFs), so giving full play to the NO oxidation activity is one of the most effective means to improve the DPF regeneration performance. In this work, based on the results of programmed temperature oxidation (TPO) experiments, Fourier transfer inference spectroscopy, and X-ray photoelectron spectroscopy, the evolution of surface functional groups was seriously analyzed to explore the soot oxidation mechanism. The results revealed that with the presence of NO in the air atmosphere, the concentration of -ONO2 groups showed an increasing trend in the early oxidation stage of 0–20 % oxidation degree (OD) and then slowly decreased during 20–80 % OD, while the variations in CH functional group concentration were directly related to the concentration NO in the air atmosphere. COO functional group is easy to decompose, and NO promotes COO's generation and decomposition. The sp3/sp2 hybrid ratio is strongly correlated with CO (carbon‑oxygen double bond), but the content of CO is also affected by the desorption of COO functional groups. It is worth noting that when the soot oxidation degree is at 50 %–80 % OD, CO groups are converted to CO functional groups.