(616a) Understanding the Reaction Mechanism on Molybdenum Carbide Species for Formation of Ethylene/Acetylene in Methane Dehydroaromatization (MDA)

In the current competitive scenario of looking out for alternate sources of fuel and chemical production, one of the potential alternates which are surfacing up is shale gas. MDA, the direct route for methane conversion is energy efficient as it eliminates the production of syngas and is a promising route to decrease the production cost of chemicals. The majority of studies highlight that Mo/HZSM-5 which is a promising catalyst in MDA shows a bifunctional mechanism. The conventional mechanism proposed in the literature did not consider carbon of Mo carbide to participate in the product formation. So, considering the dynamic nature of the active site in MDA will open a new path for the mechanism of the MDA reaction. In catalysis chemistry, the Mars Van Krevelen mechanism approach is encountered mostly and has been applied to many catalytic reactions and a similar mechanism has been extended in our study. Here in this work, by using density functional theory we are discussing how ethylene/acetylene intermediates are formed over stable Mo carbide active sites and reveal the reaction mechanism. As discussed earlier the catalyst is Mo/HZSM-5, where Mo is anchored over Al sites in the zeolite framework so the effect of support has also been studied. The Mo₂C₆ cluster was anchored on single Al atom binding through a single Mo atom in 10 membered ring (MR) of the zeolite model. Reaction and activation energies over the Mo₂C₆ cluster were calculated using the generalized gradient approximation (GGA) revised Perdew–Burke–Ernzerhof (RPBE) based exchange-correlation. Incorporating the carbon from the active site results in a lower activation barrier for C-C coupling ~55 kJ/mol. Similar trends were observed for cluster anchored over 10 MR zeolite model.