Bimetallic Pd–Au/TiO₂ Nanoparticles: An Efficient and Sustainable Heterogeneous Catalyst for Rapid Catalytic Hydrogen Transfer Reduction of Nitroarenes

Abstract

Anilines are one of the important chemical feedstocks and are utilized for the preparation of a variety of pharmaceuticals, agrochemicals, pigments, and dyes. In this context, the catalytic reduction of nitro functionality is an industrially vital process for the synthesis of aniline derivatives. Herein, we report an efficient nanosized bimetallic Pd–Au/TiO 2 nanomaterial which is proved to be quite efficient for rapid catalytic hydrogen transfer reduction of nitroarenes into corresponding amines. Significantly, the reduction process is successful under solvent-free and mild green atmospheric conditions. Bimetallic Pd–Au nanoparticles served as the active center, and TiO 2 played as a support in hydrogen transfer from the source hydrazine monohydrate. Typical results highlighted that the reactions were very rapid and the products were obtained in good to excellent yields. Significantly, the process was successful in the presence of a very low amount catalyst (0.1 mol %). Furthermore, the reaction showed good chemoselectivity and compatiblity with double or triple bond, aldehyde, ketone, and ester functionalities on the aromatic ring. Typical results indicated the true heterogeneous nature of the Pd–Au/TiO 2 nanocatalyst, where the catalyst retained the activity, without loss of its activity.

Nanoengineering of Gold Nanoparticles: Green Synthesis, Characterization, and Applications

“…Several researchers have focused on obtaining a heterostructure that improves interaction between the nanoparticles and the semiconductor oxide in order to enhance photocatalytic activity. Heterogeneous photocatalysis using AuNPs has generally been employed for the degradation of dyes [154][155][156], organic synthesis [157][158][159], and the generation of energy sources, particularly the production of hydrogen and methane [160][161][162][163].…”

Reduction of Nitroarenes via Catalytic Transfer Hydrogenation Using Formic Acid as Hydrogen Source: A Comprehensive Review

“…The first is catalyzed by specific transition metals such as iron, nickel, palladium or platinum in presence of molecular hydrogen under special pressure conditions, [8b,10–16] whereas the second strategy employs hydrogen sources for the transfer hydrogenation process such as hydrides ( e. g . NaBH 4 or hydrosilanes, [17–25] hydrazine hydrate, [17,26–30] organic reagents ( e. g . alcohol, glycerol or formic acid) [17,31–33] and more recently, boron reagents [34–35] .…”

“…morpholine, phosphorous acid); [44] however, the control of the selectivity is even persistent in the catalytic hydrogenation. As an alternative to the typical catalytic hydrogenation using H 2 for the reduction of nitro group highlights the heterogeneous catalytic transfer hydrogenation (CTH), which emerged as a more controlled strategy because the hydrogen is generated in situ using a hydrogen donor and represents a valuable strategy by their minor procedure risk, simplicity, cost‐effective and sustainability [17–35] . The design of this strategy is focused on the selection of the metallic catalyst and the hydrogen sources.…”

“…[8][9] Alternatively to Bechamp's reduction, the nitro group into nitroarene can be reduced to corresponding aromatic amines through two chemical processes: (i) the catalytic direct hydrogenation using molecular hydrogen (H 2 ) or (ii) the hydrogenation transfer using a hydrogen source. The first is catalyzed by specific transition metals such as iron, nickel, palladium or platinum in presence of molecular hydrogen under special pressure conditions, [8b,10-16] whereas the second strategy employs hydrogen sources for the transfer hydrogenation process such as hydrides (e. g. NaBH 4 or hydrosilanes, [17][18][19][20][21][22][23][24][25] hydrazine hydrate, [17,[26][27][28][29][30] organic reagents (e. g. alcohol, glycerol or formic acid) [17,[31][32][33] and more recently, boron reagents. [34][35] Other methods based on reduced sulfur reagents like elemental sulfur, [36][37] dithionite [38] or sulfides [39] are useful for the reduction of nitro group, being particularly convenient for the selective reduction of polynitroarenes.…”

Preparation of PdAuCu/C as a Highly Active Catalyst for the Reduction of 4‐Nitrophenol by Controlling the Deposition of Noble Metals

“…The catalysts could be easily recovered by a small magnet and could be reused at least seven times. Many research papers and reviews have focused on the effective catalytic reduction of 4‐NP to 4‐AP [20–50] …”