Structure and Reactivity of the Mo/ZSM-5 Dehydroaromatization Catalyst
An Operando Computational Study
Guanna Li (TU Delft - ChemE/Catalysis Engineering, TU Delft - ChemE/Inorganic Systems Engineering)
I. Vollmer (TU Delft - ChemE/Catalysis Engineering)
Chong Liu (TU Delft - ChemE/Inorganic Systems Engineering)
J. Gascon (TU Delft - ChemE/Catalysis Engineering, King Abdullah University of Science and Technology)
Evgeny Pidko (ITMO University, TU Delft - ChemE/Algemeen, TU Delft - ChemE/Inorganic Systems Engineering)
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Abstract
Mo/ZSM-5 is one of the most studied and efficient catalysts for the dehydroaromatization of methane (MDA), but the mechanism of its operation remains controversial. Here, we combine an ab initio thermodynamic analysis with a comprehensive mechanistic density functional theory study to address Mo-speciation in the zeolite and identify the active sites under the reaction conditions. We show that the exposure of Mo/ZSM-5 to the MDA conditions yields a range of reduced sites including mono- and binuclear Mo-oxo and Mo-carbide complexes. These sites can catalyze the MDA reaction via two alternative reaction channels, namely, the C-C coupling (ethylene) and the hydrocarbon-pool propagation mechanisms. Our calculations point toward the binuclear Mo-carbide species operating through the hydrocarbon-pool mechanism to be the most catalytically potent species. Although all other Mo sites in the activated catalyst can promote C-H activation in methane, they fail to provide a successful path to the desirable low-molecular-weight products.
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