Promotional effect of oxygen storage capacity on oxy-dehydrogenation of ethylbenzene with CO2 over κ-Ce2Zr2O8(111)

The effect of oxygen storage capacity on catalytic activity and stability of κ-Ce₂Zr₂O₈(111) during the oxy-dehydrogenation of ethylbenzene with CO₂ were examined by the density functional theory calculations. Results show that four kinds of lattice oxygen O_a, O_b, O_c and O_c′ existed on the κ-Ce₂Zr₂O₈(111) surface, compared with the lattice oxygen O on the CeO₂(111) surface, the order of catalytic activity is O_c′ > O_c > O_b ≈ O_a > O. By analyzing the Hirshfeld charge distribution during the CH bond activation, we find a positive correlation between the activity of lattice oxygen for the CH bond activation and the charge transferred from ethylbenzene to κ-Ce₂Zr₂O₈ catalyst. During the reaction process, surface lattice oxygen will release from κ-Ce₂Zr₂O₈(111) by reaction with H to form H₂O, which result in lattice oxygen loss and oxygen vacancy formation. However, the ability of oxygen vacancy formation on κ-Ce₂Zr₂O₈(111) is negatively correlated with its ability of CO₂ activation and dissociation, and CO₂ can hardly supply the lattice oxygen on the κ-Ce₂Zr₂O₈(111) surface with a much higher reaction barrier than CH bond activation. Taking the O_c′ of the Zr-rich termination and O_c of the Ce-rich termination as the example, the lattice oxygen from sub-surface or bulk phase can replenish the surface lattice oxygen spontaneously or just overcome a low reaction barrier of 0.26 eV, thereby maintaining the stability of the catalyst surface active site.