Initial stage of carbonization of iron during hydrocarbons dissociation: a molecular dynamics study

The carbonization of iron is a very important early phenomenon in the field of heterogeneous catalysis and the petrochemical industry, but the mechanism is still controversial. In this work, the carbonization mechanism and carbonization structure of iron nanoparticles by different carbon sources (CH4, C2H6, C2H4, C2H2) were systematically investigated using the reactive molecular dynamics method. The results show that saturated alkanes are dehydrogenated while adsorbed, but unsaturated olefins and alkynes undergo bond-breaking while adsorbed. The C-H bond is more likely to break than the C-C bond. Hydrocarbons with high carbon content have a strong ability to carbonize Fe nanoparticles under the same conditions. For C2H4 and C2H2, the C atoms generated from dissociation form a large number of long carbon chains intertwined with branched chains and multiple carbon rings. The C2 species formed by C2H2 after complete dehydrogenation diffuse rapidly to the interior of the nanoparticles, releasing the surface active sites and accelerating the carbonization process. Carbon-rich iron carbides (FeCx) with different Fe/C ratios were obtained by carbonization with different carbon sources. In addition, the Fe(110) surface exhibits the strongest carburizing ability. These findings provide systematic insights into the initial stages of metal Fe carburization.