Computational identification of bifunctional metal-modified ZSM-5 catalysts to boost methane-methanol coupling

The C-H bond activation of methane, the activation of methanol via dehydration, and methane-methanol coupling to ethylene over bifunctional metal-modified ZSM-5 catalysts were systematically investigated by density functional theory (DFT) calculations to clarify the potential roles of the introduction of methanol and the mechanism of methane-methanol coupling. Energetically favorable pathways of reactant activation and methane-methanol coupling to ethylene over M/ZSM-5 catalysts (M = Zn, Ga, Cu) are identified, and the Zn/ZSM-5 catalyst was found to exhibit superior activity for both reactant activation and C-C coupling. Comparative calculations on the C-C coupling in the absence of methanol versus methane-methanol coupling reveal that the introduction of methanol effectively promotes methane conversion due to the important role of the formed O-fra-CH3 species from methanol dehydration. The co-adsorption of H2O produced from methanol dehydration has little effect on C-C coupling and dehydrogenation to form ethylene. The present DFT results predict that adding Co, Ni, or Pd into Zn/ZSM-5 could promote this reaction due to the reduced C-C coupling barriers on these bimetallic combinations, thus becoming promising candidates for direct methane-methanol coupling.