Nickel−palladium alloy nanoparticles supported on reduced graphene oxide decorated with metallic aluminum nanoparticles (Al-rGO/NiPd): a multifunctional catalyst for the transfer hydrogenation of nitroarenes and olefins using water as a hydrogen source

Abstract

We report herein an innovative design and synthesis of a novel multifunctional nanocatalyst for the transfer hydrogenation (TH) of nitroarenes and olefins using water as a hydrogen source and solvent. The presented nanocatalyst is composed of NiPd alloy nanoparticles (NPs) supported on reduced graphene oxide (rGO) decorated with metallic Al NPs (Al-rGO/NiPd). In the catalyst, metallic Al NPs serve as the sacrificing agent for hydrogen generation via the Al-H2O reaction, NiPd NPs act as the catalyst for the transfer of the generated hydrogen to the unsaturated compounds, and rGO functions as both a support material and stabilizer for the NPs. Among all tested catalysts, Al-rGO/Ni40Pd60 nanocatalysts are found to be the most efficient and selective catalysts in the presented TH of nitroarenes (14 examples) and olefins (14 examples) with yields reaching up to 99% under the optimized reaction conditions. Additionally, Al-rGO/Ni40Pd60 nanocatalysts are recyclable catalysts in the TH reactions by catalyzing ten consecutive runs in the TH of nitrobenzene without a significant drop in their initial catalytic activity, which is the first example in this regard. Last but not least, the current transfer hydrogenation protocol provides selectivity for the reduction of only the -NO2 group of nitroarenes bearing iodo or bromo substituents on the same aromatic ring. This study is the first example of a TH protocol that employs an Al-modified nanomaterial serving as both a hydrogen generator and reusable catalyst in water without using any additional hydrogen source.