Selective catalytic hydrogenation of nitroarenes is of great importance for dyestuff and pharmaceutical industry. A critical step toward the rational design of targeted catalysts is to determine their electronic structures and related reaction mechanism. In this review, we summarize the breakthroughs on the development of multiple catalytic technologies in the past decade, including direct hydrogenation using high-pressure hydrogen; transfer hydrogenation using reductive compounds; photocatalytic hydrogenation using hole scavenger; electrocatalytic hydrogenation accompanied with water oxidation. We focus on how to understand the two key element steps including hydrogen dissociation and the activation of nitro group in the process of hydrogenation, and design and fabricate nanostructured catalysts with desired activity and selectivity. For direct catalytic hydrogenation, representative catalysts include metal, metal oxide/sulfide/carbides/nitrides/boride, and functional carbon material, and the crucial factors to tune their activity and selectivity are discussed such as metal-support interaction, size effect, alloy effect, defect engineering, and so on. Catalytic transfer hydrogenation, photocatalytic and electrocatalytic hydrogenation, in which these catalysts abstracts hydrogen species from the hydrogen donor and stabilizes it on the catalyst surface, restricting active H* recombination, and then the active hydrogen species can be promptly transferred to nitroarenes for the hydrogenation. It is worth mentioning that the light harvesting and charge separation of photocatalyst and the conductivity of electrocatalyst should also be considered together for the overall performance. All these experiences lay the foundation for large scale production of anilines and guide the rational design of catalysts for other organic transformation reactions.

Review on selective hydrogenation of nitroarene by catalytic, photocatalytic and electrocatalytic reactions

Electrochemical reduction of nitrobenzene and 4-nitrophenol in the room temperature ionic liquid [C4dmim][N(Tf)2]

The hydrogenation of nitrobenzene into aniline is one of industrially important reactions, but still remains great challenge due to the lack of highly active, chemo-selective and eco-friendly catalyst. By using extensive density functional theory (DFT) calculations, herein we predict that single Pt atom decorated g-C3N4 (Pt@g-C3N4) exhibits excellent catalytic activity and selectivity for the conversion of nitrobenzene into aniline under visible light. The overall activation energy barrier for the hydrogenation of nitrobenzene on single atom Pt@g-C3N4 catalyst is even lower than that of the bare Pt(111) surface. The dissociation of N–O bonds on single Pt atom is triggered by single hydrogen atom rather than double hydrogen atoms on the Pt(111) surface. Moreover, the Pt@g-C3N4 catalyst exhibits outstanding chemoselectivity towards the common reducible substituents, such as phenyl,–C=C,–C≡C and–CHO groups during the hydrogenation. In addition, the doped single Pt atom can significantly enhance the photoconversion efficiency by broadening the light absorption of the pristine g-C3N4 to visible light region. Our results highlight an interesting and experimentally synthesized single-atom photocatalyst (Pt@g-C3N4) for efficient hydrogenation of nitrobenzene to aniline under a sustainable and green approach.[Figure not available: see fulltext.].

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Single Pt atom decorated graphitic carbon nitride as an efficient photocatalyst for the hydrogenation of nitrobenzene into aniline

Insights into the mechanism of Nitrobenzene reduction to aniline over Pt catalyst and the significance of the adsorption of phenyl group on kinetics

This paper describes an investigation of the reduction of nitrobenzene to p-aminophenol by the use of CV, RDE and preparative electrolysis with Cu and Cu(Hg) electrodes. The preparative electrolyses of nitrobenzene were carried out at controlled current and controlled potential conditions using copper and amalgamated copper using a new semipilot (laboratory) scale system in the absence of an organic cosolvent. The effects of redox reagents and the concentration of nitrobenzene in catholyte added to the medium were also examined. The best results were obtained with 2.3% BiCl3 at nitrobenzene concentration of 0.144 g cm−3 catholyte. The most suitable electrode material was found to be amalgamated copper and the reduction of nitrobenzene to p-aminophenol was found to follow an ECE mechanism.

Electroreduction of nitrobenzene to p-aminophenol using voltammetric and semipilot scale preparative electrolysis techniques

The electrochemical reduction of nitrobenzene has been studied in aqueous organic solvents containing sulphuric acid. It is shown that the yield ofp-aminophenol and the maximum current density for the reaction is dependent upon the solvent, the cathode metal, the electrode potential, the concentration of acid and the rate of stirring of the catholyte. The changes of products would not be obvious from theI-E curves but it is possible to find conditions where the yield ofp-aminophenol is > 75% at a current density of 150 mA cm−2.

J. Marquez

Papers

A study of the electrochemical reduction of nitrobenzene to p-aminophenol