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

Ceria (CeO2) exhibits superior catalytic activityandselectivity in the hydrogenation of nitrobenzene via combination withother transition metals. However, the reaction mechanism of nitrobenzenehydrogenation by those CeO2-based catalysts is still unclear.Herein, a density functional theory study was performed to investigatethe mechanism of nitrobenzene hydrogenation by a Ni-1/CeO2-x single-atom catalyst. The dominantpathway of H-2 dissociation on the Ni-1/CeO2(111) and Ni-1/CeO2-x (111) surfaces and the oxygen vacancy formation on the Ni-1/CeO2(111) surface were proposed. The direct routeand condensation route of nitrobenzene hydrogenation on the Ni-1/CeO2-x (111) surface werefurther studied, in which the direct route includes the single H-induceddissociation pathway, the double H-induced dissociation pathway, andthe single-double H-induced mixed dissociation pathway. Thecalculated results indicate that the single-double H-inducedmixed dissociation pathway (PhNO2* & RARR; PhNOOH* & RARR;PhNO* & RARR; PhNHO* & RARR; PhNHOH* & RARR; PhNH* & RARR; PhNH2*) is the most favorable pathway for the hydrogenation ofnitrobenzene to aniline by Ni-1/CeO2-x (111). The rate-determining step of the overall reaction,using H-2 as the hydrogen source, is the fourth hydrogentransfer step (PhNHO* + H* & RARR; PhNHOH*), which has an energybarrier of 1.24 eV. This might provide theoretical insights into thenature of nitrobenzene hydrogenation to aniline by CeO2-based catalysts.