First Principles Study on the Mechanism of Nitrobenzene Hydrogenation by a Ni1/CeO2‑x(111) Single-Atom Catalyst

Ceria (CeO2) exhibits superior catalytic activity and selectivity in the hydrogenation of nitrobenzene via combination with other transition metals. However, the reaction mechanism of nitrobenzene hydrogenation by those CeO2-based catalysts is still unclear. Herein, a density functional theory study was performed to investigate the mechanism of nitrobenzene hydrogenation by a Ni1/CeO2‑x single-atom catalyst. The dominant pathway of H2 dissociation on the Ni1/CeO2(111) and Ni1/CeO2‑x (111) surfaces and the oxygen vacancy formation on the Ni1/CeO2(111) surface were proposed. The direct route and condensation route of nitrobenzene hydrogenation on the Ni1/CeO2‑x (111) surface were further studied, in which the direct route includes the single H-induced dissociation pathway, the double H-induced dissociation pathway, and the single–double H-induced mixed dissociation pathway. The calculated results indicate that the single–double H-induced mixed dissociation pathway (PhNO2* → PhNOOH* → PhNO* → PhNHO* → PhNHOH* → PhNH* → PhNH2*) is the most favorable pathway for the hydrogenation of nitrobenzene to aniline by Ni1/CeO2‑x (111). The rate-determining step of the overall reaction, using H2 as the hydrogen source, is the fourth hydrogen transfer step (PhNHO* + H* → PhNHOH*), which has an energy barrier of 1.24 eV. This might provide theoretical insights into the nature of nitrobenzene hydrogenation to aniline by CeO2-based catalysts.