Modeling phase formation on catalyst surfaces: Coke formation and suppression in hydrocarbon environments

Abstract

We develop a simulation toolset employing density functional theory in conjunction with grand canonical Monte Carlo (GCMC) to study coke formation on Fe-based catalysts during propane dehydrogenation (PDH). As expected, pure Fe surfaces develop stable graphitic coke structures and rapidly deactivate. We find that coke formation is markedly less favorable on Fe 3 C and FeS surfaces. Fe-Al alloys display varying degrees of coke resistance, depending on their composition, suggesting that they can be optimized for coke resistance under PDH conditions. Electronic structure analyses show that both electron-withdrawing effects (on Fe 3 C and FeS) and electron-donating effects (on Fe-Al alloys) destabilize adsorbed carbon. On the alloy surfaces, a geometric effect also isolates Fe sites and disrupts the formation of graphitic carbon networks. This work demonstrates the utility of GCMC for studying the formation of disordered phases on catalyst surfaces and provides insights for improving the coke resistance of Fe-based PDH catalysts.

Controlling the Coke Formation in Dehydrogenation of Propane by Adding Nickel to Supported Gallium Oxide

“…In several DFT studies, the correlation between the adsorption energy of a single carbon atom on a metallic surface and the proneness for the formation of coke was observed. In the case of Ni, this was reported for the water‐gas‐shift reaction, [85] the dry reforming of methane, [86,87] and for other transition metals and alloys in PDH [88] . These studies demonstrated that the C‐atom adsorption energy is a descriptor for the formation of coke.…”

“…In the case of Ni, this was reported for the watergas-shift reaction, [85] the dry reforming of methane, [86,87] and for other transition metals and alloys in PDH. [88] These studies demonstrated that the C-atom adsorption energy is a descriptor for the formation of coke. Here, DFT calculations were carried out to validate the coking ability of different NiGa surfaces.…”