Early Events of the Carburization of Fe Nanoparticles in Ethylene Pyrolysis: Reactive Force Field Molecular Dynamics Simulations

Abstract

The carburization of transition metals in hydrocarbon 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 carburization 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 C2H x (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 C2H x 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.

Theoretical Perspectives on the Modulation of Carbon on Transition-Metal Catalysts for Conversion of Carbon-Containing Resources

“…Without such a methodological development, reactive MD simulations, even at fairly high temperature, could only reveal the very early state of the carburization process. 59 To have a better description of the Fe−C interaction in the iron carburization process and capture the surface reactions during the carburization, we have developed a set of Fe/C/O ReaxFF 56 parameters, denoted RPOFeCO-2018. 57,60 This parameter set gives a carbon diffusion barrier of 0.70 eV in α-Fe, which is comparable to the experimental value of 0.81− 0.87 eV.…”

“…In addition, since the carburization reactions under realistic conditions are rare events, and the carburization process could last for hours or even longer experimentally, methods such as accelerated molecular dynamics are needed to go beyond the limited time scale of normal MD. Without such a methodological development, reactive MD simulations, even at fairly high temperature, could only reveal the very early state of the carburization process …”

Toward homogenous AlN via reaction of Al nanoparticles with N2 and NH3: Reactive molecular dynamics simulation

“…It should be noted that the gaseous densities of N 2 and NH 3 in this simulation are higher than those in practice in order to shorten the simulation time and to save the limited computational resources. This strategy is usually used in MD simulation 25–27 . Aluminum is directly nitrided in an N 2 or NH 3 atmosphere, and the combustion temperature of AlN rises above 3000 K 12,28 .…”

“…This strategy is usually used in MD simulation. [25][26][27] Aluminum is directly nitrided in an N 2 or NH 3 atmosphere, and the combustion temperature of AlN rises above 3000 K. 12,28 All RMD simulations were performed in the NVT canonical ensemble (particle numbers, volume and temperature in constant). First, the simulation was carried out for 10 ps at 298 K, then the system was heated to the target temperature within 30 ps.…”

Sintering Mechanism of Core@Shell Metal@Metal Oxide Nanoparticles

“…We performed all the sintering MD simulations using the ReaxFF reactive force field developed by van Duin et al The ReaxFF potentials are suitable for modeling complex processes such as nucleation and growth of nanoparticles. , The ReaxFF force fields for Ni/O, Fe/O, and Cu/O were extracted from Shin et al, Shin et al, and van Duin et al, respectively. The force fields used in this study are parametrized for bulk or bulk surface properties of the metals; however, they have been successfully employed for simulations involving metal nanoparticles. − ReaxFF potentials parametrized for bulk materials are routinely utilized for investigating properties not only of bulk surfaces but also of nanoparticles. − …”