Insights into Different Products of Nitrosobenzene and Nitrobenzene Hydrogenation on Pd(111) under Realistic Reaction Conditions

Abstract

Selective hydrogenation of nitroarene compounds is applied in many fields such as agrochemicals, pharmaceuticals, and dyes. Pd-catalyzed hydrogenation of nitrobenzene (PhNO2) and nitrosobenzene (PhNO) could exhibit different selectivities. This was regarded as the evidence to challenge the Haber mechanism for PhNO2 hydrogenation in which PhNO is an important intermediate. In this study, we systematically investigate their hydrogenation mechanisms under realistic reaction conditions based on first-principles calculations. It is found that the weak bonding between the nitro group and the Pd(111) surface leads to the flat-lying chemisorption configuration of PhNO2 and the other intermediates during PhNO2 hydrogenation. In contrast, the strong bonding between the nitroso group and the surface makes PhNO switch its chemisorption mode from flat-lying adsorption under the ultrahigh vacuum condition to vertical adsorption under reaction conditions. For the flat-lying PhNO2, the chemisorbed phenyl group makes hydrogenation easier but hinders N–O bond breaking, resulting in the production of PhNH2 via a direct pathway. Conversely, without the hinderance of the chemisorbed phenyl group, N–O bond breaking and N–N coupling become more favorable during the reduction of vertical PhNO* toward the formation of azoxy compound on Pd(111). These results unveil the fact that the difference between the selectivities of PhNO2 and PhNO hydrogenation is independent of the formation of PhNO* but dependent on the phenyl group adsorption mode.

Reduction of Nitro Compounds Using 3d-Non-Noble Metal Catalysts

“…[37][38][39][40][41] Despite the relevance of the reduction of nitro compounds, only few studies on the reaction mechanism were published during the years and the majority of them dealt with heterogeneous noble metal catalysts (mainly based on Pd, Pt, Au and Rh). 17,[42][43][44] As a consequence, the mechanism reported by Haber still continues to represent the main reference for describing the possible reaction pathways, even in the case of non-noble metal catalysts. An exception is represented by Ni-based heterogeneous catalysts, for which two studies were very recently reported and will be discussed in the dedicated chapter.…”

Promoting H2 Activation over Molybdenum Carbide by Modulation of Metal‐Support Interaction for Efficient Catalytic Hydrogenation

“…The whole reaction is exothermic (−1.85 eV), indicating that the nitrobenzene hydrogenation on the Mo 2 C/NC surface is thermodynamically favored (Table S4). Noteworthily, the whole reaction energy can even rival that for previously reported Pd(111) (−1.38 eV), revealing that the activity of Mo 2 C/NC is comparable to that of noble‐metal based catalysts in hydrogenation of nitrobenzene to aniline [40a] …”

Atomically dispersed and oxygen deficient CuO clusters as an extremely efficient heterogeneous catalyst

“…The overall pathway of 4-NP reduction can be described as: C 6 H 5 NO 2 → C 6 H 5 NOOH* → C 6 H 5 NO* → C 6 H 5 NOH* → C 6 H 5 N* → C 6 H 5 NH* → C 6 H 5 NH 2 . 45,46 The reaction from the initial NO 2 − to the final NH 2 − is accompanied with a sharp 4.3 eV decline in energy. Nitrosobenzene (PhNO) is considered a key intermediate for the calculations, and the detailed results are given in the ESI (Fig.…”

“…S16-S18 †). 45 For the first stage, the energy for the adsorption (E ads ) of 4-NP on the (110) surface of CuO and OVs-CuO is −0.68 and −0.73 eV, respectively (Fig. 5b).…”

“…† The catalytic reduction of 4-NP includes two stages: (1) the adsorption of 4-NP and (2) the activation and cleavage of the N-O bond. The overall pathway of 4-NP reduction can be described as: 45,46 The reaction from the initial NO 2 − to the final NH 2 − is accompanied with a sharp 4.3 eV decline in energy. Nitrosobenzene (PhNO) is considered a key intermediate for the calculations, and the detailed results are given in the ESI (Fig.…”