Correlation between the Properties of Surface Lattice Oxygen on NiO and Its Reactivity and Selectivity towards the Oxidative Dehydrogenation of Propane

Abstract

Modified NiO catalysts with controllable vacancies and dopants are promising for alkene production from oxidative dehydrogenation (ODH) of light alkanes, and a molecular understanding of the modification on elementary reaction steps would facilitate the design of highly efficient catalysts and catalytic processes. In this study, density functional theory (DFT) calculations was used to map out the complete reaction pathways of propane ODH on the NiO (100) surfaces with different modifiers. The results demonstrated that the presence of vacancies (O and Ni) and dopants (Li and Al) alters the electrophilicity of surface oxygen species, which in turn affects the reactivity towards C−H bond activation and the overall catalytic activity and selectivity. The strongly electrophilic O favors a radical mechanism for the first C−H activation on O followed by the second C−H activation on O−O site, whereas weak electrophilic O favors concerted C−H bond breaking over Ni−O site. The C−H bond activation proceeds through a late transition state, characterized by the almost completion of the O−H bond formation. Consequently, the adsorption energy of H adatom on O rather than p‐band center or Bader charge of O has been identified to be an accurate descriptor to predict the activation barrier for C−H breaking (activity) as well as the difference between the activation barriers of propene and CH3CCH3 (selectivity) of ODH.

Facet-Dependent Oxygen Mobility and Reaction Pathways for Oxidative Dehydrogenation of 1-Butene over Bi2MoO6

“…The abstraction of the second H must overcome a high activation energy of 2.59 eV. The activation of the C–H bonds on both {001} and {010} facets follows the radical mechanism . Subsequently, the formed water and 1,3-butadiene molecules desorb from the surface, respectively.…”

“…The activation of the C−H bonds on both {001} and {010} facets follows the radical mechanism. 50 Subsequently, the formed water and 1,3butadiene molecules desorb from the surface, respectively. The rate-determining step on the {010} facet is the abstraction of the second H. The rupture of both of the C−H bonds on the {010} facet is more difficult than that on the {001} facet.…”