Role of oxygen vacancy in cobalt doped ceria catalyst for styrene epoxidation using molecular oxygen

The oxygen vacancy formation and refillment of oxygen vacancy by molecular oxygen are the key steps of catalyst redox cycle towards styrene epoxidation reaction. Well dispersed, Isomorphically substituted and energetically favorable cobalt based redox cycle in ceria lattice caused lower oxygen formation energy, oxygen adsorption energy and activation energy than pure ceria for the reaction ensuring excellent catalytic activity. DFT studies show that inclusion of cobalt in ceria leads to lower the oxygen removal energy. Oxygen vacancy formation resulted into the rise of the spin magnetic moment of cobalt to 2.70 μB indicating reduction of Co⁺³ to Co⁺² as well as fall of oxygen adsorption energy. A mechanistic proposal is presented in which Co³⁺/Co²⁺, Ce⁴⁺/Ce³⁺, oxygen vacancies are involved in adsorption, activation reaction of oxygen and styrene on the surface of the catalyst. The Co(4)-CeO₂ catalyst also demonstrated reactivity towards stilbene, cyclooctene under similar reaction condition. The catalyst was regenerated up to three cycles.