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

Abstract

We develop a simulation toolset employing density functional theory\n(DFT) in conjunction with grand canonical Monte Carlo (GCMC) to study\ncoke formation on Fe-based catalysts during propane dehydrogenation\n(PDH). As expected, pure Fe surfaces develop stable graphitic coke\nstructures and rapidly deactivate. We find that coke formation is\nmarkedly less favorable on FeC and FeS surfaces. Fe-Al\nalloys display varying degrees of coke resistance, depending on their\ncomposition, suggesting that they can be optimized for coke resistance\nunder PDH conditions. Electronic structure analyses show that both\nelectron-withdrawing effects (on FeC and FeS) and\nelectron-donating effects (on Fe-Al alloys) destabilize adsorbed carbon.\nOn the alloy surfaces, a geometric effect also isolates Fe sites and\ndisrupts the formation of graphitic carbon networks. This work\ndemonstrates the utility of GCMC for studying the formation of\ndisordered phases on catalyst surfaces and provides insights for\nimproving the coke resistance of Fe-based PDH catalysts.