A ReaxFF Molecular Dynamics Study of Interactions Between Iron- Containing Nanoparticles and Soot Precursors

QY He and Y Li and XQ You, COMBUSTION SCIENCE AND TECHNOLOGY (2025).

DOI: 10.1080/00102202.2025.2520796

In this work, we performed a ReaxFF molecular dynamics study of the interactions between soot precursors (e.g. C2H2, benzene, and pyrene) and iron-containing nanoparticles (Fe, Fe2O3, and FeO) to better understand the "core-shell" particles observed in experiments. It was found that after simulating 1000 ps at 1673 K, iron-containing nanoparticles partially transform into Fe-C sosoloid, which is characterized by carbon (C) atoms embedded in the nanoparticles and locally regularly arranged with Fe atoms. The extent of transformation to Fe-C sosoloid depends on the precursor adsorption rates on the nanoparticles. To further investigate the precursor adsorption process and the formation of Fe-C sosoloid, we then studied the mechanism of pyrene adsorption on Fe nanoparticles over a wide temperature range of 300-2400 K. The settings of the simulation cases, including pyrene concentration and Fe nanoparticle size, were obtained from previous experimental work on the effect of FeCl3 addition on soot formation in ethylene pyrolysis. The simulation results showed that pyrene molecules were chemically adsorbed on the Fe nanoparticle after the nanoparticle abstracted H atoms in pyrene, and the adsorption capacity of the nanoparticle increased with increasing temperature. At lower temperatures (<1500 K), the pyrenyl groups were found to be bound to the surface of the nanoparticle, while with further increase in temperature, the transition to the Fe-C sosoloid occurred. Above 1800 K, the Fe-C sosoloid was formed within 1000 ps simulation time with a fixed Fe/C number ratio of 3/8, limiting further chemical adsorption of pyrene by the iron-containing nanoparticles.

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