On the Mechanisms of Carbon Formation Reaction on Ni(111) Surface

The carbon formation reaction (abbreviated in this work from now on as CFR) is an industrially important chemical process. Using density functional theory, we explored the detailed mechanisms of the process on the Ni(111) surface. Four possible reaction pathways that give rise to carbon deposition on the surface were examined based on minimum energy path calculations. It was found that both the direct dissociation of CO on the surface and the pathway in which a gas phase H2 molecule reacts with an adsorbed CO molecule to produce a gas phase water molecule and a C adatom are kinetically difficult due to the high activation energies. It was identified that the rate limiting step along the reaction pathway is CO* + 2H* → HCO* + H*. Comparison of the calculated energetic profiles of the CFR process on both the Ni(111) and the γ-Fe(111) surfaces was also made. Both the H atom and the CO moiety exhibit high mobility on the surfaces after adsorption, which allows them to readily react with various surface species. We found that the Ni(111) surface is capable of blocking the sequential surface reactions in the early stages, in contrast to the surface processes on the γ-Fe(111) surface. This suggests that nickel is more resistant against carbon formation than iron, which is consistent with experimental observations.