Monomolecular Dehydration of Ethanol into Ethylene over H-MOR Studied by Density Functional Theory.

The framework effect of H-mordenite (H-MOR) zeolite on monomolecular dehydration of ethanol to ethylene has been simulated based on density functional theory. It is indicated that both the reaction mechanism and the activation energy barriers are significantly affected by the pore-confinement effect. In the 12-membered ring (12-MR), the energy barriers of the stepwise mechanism and the concerted mechanism are 35.0 and 42.4 kcal mol, respectively, suggesting that ethylene can be competitively formed through both pathways. While in the 8-membered ring (8-MR), the barrier of the concerted mechanism is 43.4 kcal mol, which is much lower than that of the stepwise mechanism with the ethoxy intermediate formation barrier of 53.7 kcal mol. Furthermore, the water molecule acts as the intermediate to stabilize the transition states (TSs) for both stepwise and concerted mechanisms and helps to transport protons during the reaction.