High selective catalyst for ethylene epoxidation to ethylene oxide: A DFT investigation

Abstract

Ethylene epoxidation to produce ethylene oxide is crucial in both fundamental knowledge and industrial chemical process. The reaction mechanism of ethylene epoxidation with N2O catalyzed by Mn-coordinated porphyrin-like graphene (Mn-N4GP) was investigated using dispersion-corrected density functional theory calculations. The reaction proceeds through two consecutive steps, (1) MnO active site (MnO-N4GP) formation, followed by (2) ethylene epoxidation on the MnO. The first step is a feasible process with the energy barrier of 0.77 eV and the MnO-N4GP is thermodynamically stable. The ethylene epoxidation in the second step competitively can undergo three possible intermediate-pathways; carboradical, alkoxide radical, and manganaoxetane intermediates. By systematic study of all possible pathways, we found that the pathway for alkoxide radical intermediate shows the most feasibility which it subsequently converts to three competitive products with the energy barriers of 0.25 eV, 0.56 eV, and 0.46 eV for the formation of ethylene oxide, acetaldehyde, and 5-membered ring (5MR) species, respectively. This catalyst is remarkably selective to ethylene oxide by 105 and 104 times compared with acetaldehyde and 5MR side products, respectively. Thus, the Mn-N4GP catalyst is suggested as a promising catalyst in terms of activity and selectivity for ethylene epoxidation using N2O as an oxidizing agent in mild condition.