Impact of NO on soot oxidation under gasoline direct injection engines exhaust condition

The oxidation of soot under gasoline direct injection (GDI) engines exhaust conditions plays a critical role in particulate emission control. However, the impact of nitric oxide (NO) on this process remains insufficiently understood. This study combines experimental characterization, density functional theory (DFT) calculations, and kinetic simulations to investigate the inhibitory effect of NO on soot oxidation. Compared to oxidation in O 2 alone, the presence of NO suppresses oxidation by occupying active sites and blocking the reaction between O 2 and soot. This site-blocking effect leads to reduced oxidation reactivity and noticeable changes in soot properties, including decreased surface oxygen content and inhibited graphitization. Online mass spectrometry reveals increased O 2 signal upon NO introduction, confirming site-blocking behavior. DFT calculations indicate that NO tends to form C(NO) species following adsorption, which are kinetically unfavorable for further oxidation due to their high activation barriers. Combined with kinetic simulations, the calculation results further support that C(NO) occupies active sites, preventing access by more reactive O 2 —consistent with the observed increase in O 2 concentration and the decrease in surface oxygen content in the presence of NO The reversibility of NO inhibition is attributed to the rapid decomposition of C(NO), which can release NO and restore active sites. Novelty and significance statement The novelty of this study lies in unveiling the inhibitory effect of NO on soot oxidation under GDI engine exhaust condition. It provides a comprehensive understanding of the inhibition mechanism by combining experimental analyses of soot physicochemical properties with theoretical calculations. This work is significant in advancing the fundamental understanding of oxidation reactions in carbonaceous materials and offers theoretical insights for developing emission reduction strategies.