Mars-van Krevelen-like Mechanism of CO Hydrogenation on an Iron Carbide Surface

Abstract

Computational chemistry is used to explore a mechanism for CO hydrogenation to methane on iron carbides. As CO dissociation is endothermic on carbon terminated Fe 5 C 2 (100) cuts, we explore a path starting with the hydrogenation of the surface, which liberates iron 4-fold sites for adsorption and dissociation of CO. The reaction cycle to methane resembles the Mars-van Krevelen mechanism for oxidation reactions.

Reflections on the Fischer-Tropsch synthesis: Mechanistic issues from a surface science perspective

“…alkyls, alkenyls, etc) have been made, where organometallic chemistry has been used for inspiration [11,12]. In the case of iron, the active phase is a carbide, where the lattice carbon atoms in the surface region are likely to be involved in the reaction mechanism [13][14][15][16][17]. Nevertheless, similar mechanistic issues play a role as in the mechanism over metallic FTS catalysts.…”

The role of potassium promoter in surface carbon hydrogenation on Hägg carbide surfaces

“…Previous studies showed that surface carbon hydrogenation is easier than CO direct dissociation on the perfect Fe x C y surfaces [42][43][44], and monomer (CH x ) formation from surface carbon hydrogenation on iron carbide surfaces via the Mars-van-Krevelen mechanism was found accessible [45]. The consumption of surface carbon atoms results in the formation of surface vacancies which can enhance CO adsorption and largely lower CO dissociation barriers.…”

Elementary steps of syngas reactions on Mo2C(001): Adsorption thermochemistry and bond dissociation

“…These reactions are traditionally catalyzed with transition metals which often suffer from high cost, poisoning, graphitization, or carburization [1,9,3,2,10] . The use of transition metal carbides as catalysts presents an interesting alternative due to the possibility of unique Mars-van-Krevelen type mechanisms [11], inherent stability against bulk carburization, and potentially lower costs [3]. Carbide catalysts have been the subject of numerous theoretical and experimental investigations since their activity was compared to platinum by Levy and Boudart [12], and have proven to be active for many different reactions [8,3,13].…”