Unraveling the facet-dependent and oxygen vacancy role for ethylene hydrogenation on Co₃O₄ (110) surface: A DFT+U study

Highlights: • The mechanism of ethylene hydrogenation on perfect and oxygen defective Co₃O₄(110) is investigated by using DFT + U. • Oxygen vacancy promotes ethylene hydrogenation thermodynamically and kinetically. • The Co3O4 (110) facet is more active than the (111) one for ethylene hydrogenation. - Abstract: Crystal facet engineering and defect engineering are both critical strategies to improve the catalytic hydrogenation performance of catalyst. Herein, ethylene hydrogenation on the perfect and oxygen defective Co₃O₄(110) surfaces has been studied by using periodic density functional theory calculations. The results are compared with that on Co₃O₄(111) surface to clarify the problem of which facet for Co₃O₄ is more reactive, and to illuminate the role of oxygen vacancy. The low oxygen vacancy formation energy suggests that Co₃O₄(110) surface with defective site is easily formed. The whole mechanism of H₂ dissociation and stepwise hydrogenation of ethylene to ethane is examined, and the most favorable pathway is heterolytic dissociation of H₂ follows two stepwise hydrogenation of ethylene process. The results show that ethyl hydrogenation to ethane on perfect Co₃O₄(110) surface is the rate limiting step with an activation energy of 1.19 eV, and the presence of oxygen vacancy strongly reduces the activation energies of main elementary steps, and the activation energy of rate limiting step is only 0.47 eV. Compared with that on Co₃O₄(111), ethylene hydrogenation is preferred on Co₃O₄(110) surface. Therefore, Co₃O₄ with exposed (110) facet is predicted as an excellent catalyst for ethylene hydrogenation.