Co-CeO2 Interaction Induces the Mars-van Krevelen Mechanism in Dehydrogenation of Ethane

Introducing a catalyst for dehydrogenation of ethane (EDH) for steam cracking represents a promising solution with high feasibility to realize efficient ethylene production. We investigated EDH over transition-metal-doped CeO2 catalysts at 873 K in the presence of steam. Ce0.8Co0.2O2 exhibited high EDH activity and selectivity to ethylene (ca. 95%). In the absence of H2O, the catalytic activity dropped rapidly, indicating the promotive effect of H2O on ethylene formation. Catalytic experiments with water isotopes (D2O and (H2O)-O-18) demonstrated that EDH over Ce0.8Co0.2O2 proceeds through the Mars-van Krevelen (MvK) mechanism in which the reactive lattice oxygen in Ce0.8Co0.2O2 contributes to EDH. The consumed lattice oxygen was subsequently regenerated with H2O. X-ray diffraction and in situ X-ray absorption fine structure spectroscopy revealed that cobalt species were mainly present as CoO under EDH conditions and that redox between Co2+ and CoO proceeded concomitantly with EDH. In contrast with Ce0.8Co0.2O2, no contribution of the lattice oxygen of CoO to EDH was verified in the case of CoO supported on alpha-Al2O3, which exhibited lower activity than Ce0.8Co0.2O2. Therefore, Co-CeO2 interactions are expected to play a crucially important role in controlling the characteristics of the reactive lattice oxygen suitable for EDH via the MvK mechanism.