Highly chemoselective reduction of aromatic nitro compounds by copper nanoparticles/ammonium formate

Catalytic reduction of 4-nitrophenol using gold nanoparticles biosynthesized by cell-free extracts of Aspergillus sp. WL-Au

A facile one-pot eco-friendly process for synthesis of gold nanoparticles (AuNPs) with high catalytic activity was achieved using cell-free extracts of Aspergillus sp. WL-Au as reducing, capping and stabilizing agents. The surface plasmon resonance band of UV-vis spectrum at 532nm confirmed the presence of AuNPs. Transmission electron microscopy images showed that quite uniform spherical AuNPs were synthesized and the average size of nanoparticles increased from 4nm to 29nm with reaction time. X-ray diffraction analysis verified the formation of nano-crystalline gold particles. Fourier transform infrared spectra showed the presence of functional groups on the surface of biosynthesized AuNPs, such as OH, NH, CO, CH, COH and COC groups, which increased the stability of AuNPs. The biogenic AuNPs could serve as a highly efficient catalyst for 4-nitrophenol reduction. The reaction rate constant was linearly correlated with the concentration of AuNPs, which increased from 0.59min^-1 to 1.51min^-1 with the amount of AuNPs increasing form 1.46×10^-6 to 17.47×10^-6mmol. Moreover, the as-synthesized AuNPs exhibited a remarkable normalized catalytic activity (4.04×10⁵min^-1mol^-1), which was much higher than that observed for AuNPs synthesized by other biological and conventional chemical methods.

Copper-coordination polymer-controlled Cu@N-rGO and CuO@C nanoparticle formation: reusable green catalyst for A3-coupling and nitroarene-reduction reactions

Cu/CuO NPs were fabricated in N-rGO/carbon matrices using structural versatility of coordination polymers and utilized as reusable green catalyst.

Heterogenized Bimetallic Pd-Pt-Fe3O4 Nanoflakes as Extremely Robust, Magnetically Recyclable Catalysts for Chemoselective Nitroarene Reduction

A very simple synthesis of bimetallic Pd-Pt-Fe3O4 nanoflake-shaped alloy nanoparticles (NPs) for cascade catalytic reactions such as dehydrogenation of ammonia-borane (AB) followed by the reduction of nitro compounds (R-NO2) to anilines or alkylamines (R-NH2) in methanol at ambient temperature is described. The Pd-Pt-Fe3O4 NPs were easily prepared via a solution phase hydrothermal method involving the simple one-pot coreduction of potassium tetrachloroplatinate (II) and palladium chloride (II) in polyvinylpyrrolidone with subsequent deposition on commercially available Fe3O4 NPs. The bimetallic Pd-Pt alloy NPs decorated on Fe3O4 NPs provide a unique synergistic effect for the catalysis of cascade dehydrogenation/reduction. Various nitroarene derivatives were reduced to anilines with very specific chemoselectivity in the presence of other reducible functional groups. The bimetallic Pd-Pt-Fe3O4 NPs provide a unique synergistic effect for the catalysis of cascade dehydrogenation/reduction. The nitro reduction proceeded in 5 min with nearly quantitative conversions and yields. Furthermore, the magnetically recyclable nanocatalysts were readily separated using an external magnet and reused up to 250 times without any loss of catalytic activity. A larger scale (10 mmol) reaction was also successfully performed with >99% yield. This efficient, recyclable Pd-Pt-Fe3O4 NPs system can therefore be repetitively utilized for the reduction of various nitro-containing compounds.

A ternary Cu2O-Cu-CuO nanocomposite: a catalyst with intriguing activity

In this work, the syntheses of Cu2O as well as Cu(0) nanoparticle catalysts are presented. Copper acetate monohydrate produced two distinctly different catalyst particles with varying concentrations of hydrazine hydrate at room temperature without using any surfactant or support. Then both of them were employed separately for 4-nitrophenol reduction in aqueous solution in the presence of sodium borohydride at room temperature. To our surprise, it was noticed that the catalytic activity of Cu2O was much higher than that of the metal Cu(0) nanoparticles. We have confirmed the reason for the exceptionally high catalytic activity of cuprous oxide nanoparticles over other noble metal nanoparticles for 4-nitrophenol reduction. A plausible mechanism has been reported. The unusual activity of Cu2O nanoparticles in the reduction reaction has been observed because of the in situ generated ternary nanocomposite, Cu2O-Cu-CuO, which rapidly relays electrons and acts as a better catalyst. In this ternary composite, highly active in situ generated Cu(0) is proved to be responsible for the hydride transfer reaction. The mechanism of 4-nitrophenol reduction has been established from supporting TEM studies. To further support our proposition, we have prepared a compositionally similar Cu2O-Cu-CuO nanocomposite using Cu2O and sodium borohydride which however displayed lower rate of reduction than that of the in situ produced ternary nanocomposite. The evolution of isolated Cu(0) nanoparticles for 4-nitrophenol reduction from Cu2O under surfactant-free condition has also been taken into consideration. The synthetic procedures of cuprous oxide as well as its catalytic activity in the reduction of 4-nitrophenol are very convenient, fast, cost-effective, and easily operable in aqueous medium and were followed spectrophotometrically. Additionally, the Cu2O-catalyzed 4-nitrophenol reduction methodology was extended further to the reduction of electronically diverse nitroarenes. This concise catalytic process in aqueous medium at room temperature revealed an unprecedented catalytic performance which would draw attention across the whole research community.

An abnormal N-heterocyclic carbene based nickel complex for catalytic reduction of nitroarenes

The NiCl₂(aNHC)₂ complex has been used as an efficient catalyst for the reduction of nitroarenes with hydrosilanes to give aromatic amines in good to excellent yields.

Reduction of selective polyaromatic nitrotriptycene via an azoxytriptycene intermediate under ambient conditions using a cobalt/cobalt oxide nanocomposite (CoNC)

Selectively targeted polyaromatic 2-nitrotriptycene (M1) and 2,6,14-trinitrotriptycene (M2) were chosen as model substrates for demonstrating catalytic hydrogenation, under ambient conditions, using a cobalt/cobalt oxide based nanocomposite (CoNC) as the catalytic material.

Cu ion-exchanged and Cu nanoparticles decorated mesoporous ZSM-5 catalysts for the activation and utilization of phenylacetylene in a sustainable chemical synthesis

Highly dispersed Cu nanoparticles supported on the large external surface of Meso-ZSM-5 exhibited excellent activity in the selective synthesis of indolizines, chalcones, and triazoles using phenylacetylene as one of the building blocks.

Environmentally benign selective hydrogenation of α,β-unsaturated aldehydes and reduction of aromatic nitro compounds using Cu based bimetallic nanoparticles supported on multiwalled carbon nanotubes and mesoporous carbon

The catalytic activity of these materials was investigated in the hydrogenation of α,β-unsaturated aldehydes and reduction of aromatic nitro compounds using different hydrogen sources.

Facile one-pot tandem reductive amination of aldehydes from nitroarenes over a hierarchical ZSM-5 zeolite containing palladium nanoparticles

Palladium nanoparticles embedded in hierarchical zeolite act as an acid–metal bifunctional catalyst for efficient reductive amination of aldehyde from nitroarenes.

A simple and efficient in situ generated ruthenium catalyst for chemoselective transfer hydrogenation of nitroarenes: kinetic and mechanistic studies and comparison with iridium systems

A convenient and highly efficient in situ generated Ru(ii) system for synthesizing functionalized amines and mechanistic studies and comparison with iridium systems is presented.

Cu–Pd/γ-Al2O3 catalyzed the coupling of multi-step reactions: direct synthesis of benzimidazole derivatives

Catalyzed by the synergy effects of Cu–Pd bimetal and acidity of γ-Al₂O₃, the transfer hydrogenation and successive cyclization coupling reaction from o-nitroaniline and alcohol to afford benzimidazole derivatives in high yield was realized.

Gum acacia–CuNp–silica hybrid: an effective, stable and recyclable catalyst for reduction of nitroarenes

The catalytic properties gum acacia–CuNps–silica hybrid was investigated in reduction of nitroarenes.

Lamellar Ni/Al-SBA-15 fibers: preparation, characterization, and applications as highly efficient catalysts for amine and imine syntheses

A novel lamellar Ni/Al-SBA-15 fiber catalyst was prepared and successfully utilized in one-pot syntheses of amines and imines.

Preparation and characterization of Ni/mZSM-5 zeolite with a hierarchical pore structure by using KIT-6 as silica template: an efficient bi-functional catalyst for the reduction of nitro aromatic compounds

Ni/mZSM-5 hierarchical zeolite and the acidic form of it were prepared as novel bi-functional catalysts which showed excellent activity for reduction of nitro aromatic compounds in aqueous medium at room temperature.

Magnetically separable core–shell iron oxide@nickel nanoparticles as high-performance recyclable catalysts for chemoselective reduction of nitroaromatics

A magnetically separable core–shell iron oxide@nickel nanocatalyst was synthesized, characterized and applied for the aromatic nitro group reduction.

Highly efficient and selective photocatalytic reduction of nitroarenes using the Ni2P/CdS catalyst under visible-light irradiation

A highly efficient Ni₂P/CdS photocatalytic system in water for selective nitro reduction to amino organics and the reaction mechanism were presented clearly.

Direct vs. indirect pathway for nitrobenzene reduction reaction on a Ni catalyst surface: a density functional study

Density functional theory (DFT) calculations are performed to understand and address the previous experimental results that showed the reduction of nitrobenzene to aniline prefers direct over indirect reaction pathways irrespective of the catalyst surface. Nitrobenzene to aniline conversion occurs via the hydroxyl amine intermediate (direct pathway) or via the azoxybenzene intermediate (indirect pathway). Through our computational study we calculated the spin polarized and dispersion corrected reaction energies and activation barriers corresponding to various reaction pathways for the reduction of nitrobenzene to aniline over a Ni catalyst surface. The adsorption behaviour of the substrate, nitrobenzene, on the catalyst surface was also considered and the energetically most preferable structural orientation was elucidated. Our study indicates that the parallel adsorption behaviour of the molecules over a catalyst surface is preferable over vertical adsorption behaviour. Based on the reaction energies and activation barrier of the various elementary steps involved in direct or indirect reaction pathways, we find that the direct reduction pathway of nitrobenzene over the Ni(111) catalyst surface is more favourable than the indirect reaction pathway.

Nano Cu-catalyzed efficient and selective reduction of nitroarenes under combined microwave and ultrasound irradiation

In situ preparation of copper nanoparticles from a copper acetate precursor and its application as an efficient catalyst for the selective reduction of aromatic nitro compounds with hydrazine hydrate under combined microwave and ultrasound irradiation were described in detail. The results reveal the synergetic effect of microwave and ultrasound on the synthesis of copper nanoparticles, and formation of various amino derivatives.

Efficient thermal- and photocatalyst of Pd nanoparticles on TiO₂ achieved by an oxygen vacancies promoted synthesis strategy

Pd nanoparticles supported on defective TiO2 with oxygen vacancies (TiO2-OV) have been prepared by an oxygen vacancies mediated reduction strategy. The resulting Pd-TiO2-OV catalyst with uniform Pd nanoparticles deposition demonstrates a remarkably thermocatalytic activity toward rapid, efficient reduction of nitroaromatics in water. The reaction proceeds efficiently using HCOONH4 as a hydrogen source under ambient conditions. The controlled experiments show that the (•)CO2(-) radicals produced by dehydrogenation of HCOONH4 are the main active species for the selective nitro reduction. Moreover, defective TiO2 nanostructures deposited with Pd nanoparticles, featuring excellent visible-light absorption via the creation of oxygen vacancies, can take advantage of the solar and thermal energy to drive catalytic reduction reactions more efficiently at room temperature. During this process, the oxygen vacancies and Pd nanoparticles play synergetic roles in the photoreduction of nitro compounds. Our work would be beneficial for implementation of a novel defect-mediated catalytic system in which solar light energy can be coupled with thermal energy to drive an energy efficient catalytic process.

RhNPs/SBA-NH2: a high-performance catalyst for aqueous phase reduction of nitroarenes to aminoarenes at room temperature

A RhNPs/SBA-NH₂ catalyst with <3 nm sized nanoparticles has been synthesized and used in the chemoselective hydrogenation of nitroarenes at room temperature in aqueous medium with N₂H₄·H₂O with high TOF.

Polymethylhydrosiloxane derived palladium nanoparticles for chemo- and regioselective hydrogenation of aliphatic and aromatic nitro compounds in water

Chemo- and regioselective hydrogenation of a wide range of nitro compounds has been achieved with polysiloxane-stabilised ''Pd'' nanoparticles and PMHS in water.

Synergistic effect from Lewis acid and the Ni–W2C/AC catalyst for highly active and selective hydrogenation of aryl nitro to aryl amine

Highly-active and selective hydrogenation of nitroarenes to their corresponding aromatic amines by synergism from Ni–W₂C/AC and Lewis acid is presented.

A novel magnetic Fe@Au core-shell nanoparticles anchored graphene oxide recyclable nanocatalyst for the reduction of nitrophenol compounds

In this study, a novel catalyst based on Fe@Au bimetallic nanoparticles involved graphene oxide was prepared and characterized by transmission electron microscope (TEM), and x-ray photoelectron spectroscopy (XPS). The nanomaterial was used in catalytic reductions of 4-nitrophenol and 2-nitrophenol in the presence of sodium borohydride. The experimental parameters such as temperature, the dosage of catalyst and the concentration of sodium borohydride were studied. The rates of catalytic reduction of the nitrophenol compounds have been found as the sequence: 4-nitrophenol>2-nitrophenol. The kinetic and thermodynamic parameters of nitrophenol compounds were determined. Activation energies were found as 2.33 kcal mol(-1) and 3.16 kcal mol(-1) for 4-nitrophenol and 2-nitrophenol, respectively. The nanomaterial was separated from the product by using a magnet and recycled after the reduction of nitrophenol compounds. The recyclable of the nanocatalyst is economically significant in industry.