Early Events of the Carburization of Fe Nanoparticles in Ethylene Pyrolysis: Reactive Force Field Molecular Dynamics Simulations
XY Wang and XG Xue and CY Zhang, JOURNAL OF PHYSICAL CHEMISTRY C, 122, 10835-10845 (2018).
The carburization of transition metals in hydro-carbon pyrolysis is a common corrosion phenomenon in the petrochemical industry. Nevertheless, early events of carburization mechanism remain still unclear. The present work reveals the details at earlier stages of the Fe nanoparticles carburization in ethylene (C2H4) pyrolysis with reactive ReaxFF force field molecular dynamics simulations. Our results show that the chemisorption and dissociation of C2H4 on Fe surfaces are crucial steps to the carbunzation corrosion. First of all, C2H4 molecules are chemically adsorbed on the surface of the Fe nanoparticle. Afterward, continuous dehydrogenation of C2H4 occurs by C-H bond break to form C2Hx (x = 0-3). And finally, an amorphous C-rich carbide FeC3.39 is obtained. The carbide formation proceeds in four sequential and repetitive stages, including chemisorption and dehydrogenation of C2H4 on the surface of the Fe nanoparticle, diffusion and polymerization of C2Hx to form short C chains on the surface and in the bulk of the particle, growth and branching of the short chains, and chain cross-linking to form longer and more branched chains. Our finding provides deep insight into the fundamental process of carburization corrosion of Fe nanoparticles in the hydrocarbon pyrolysis, as a common phenomenon observed in practice.
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