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

Nickel ferrite decorated noble metal containing nitrogen-doped carbon nanotubes as potential magnetic separable catalyst for dinitrotoluene hydrogenation

The 2,4-toluenediamine (TDA) is one of the most important chemicals in the polyurethane industry, produced by the catalytic hydrogenation of 2,4-dinitrotoluene (DNT). The development of novel catalysts that can be easily recovered from the reaction mixture is of paramount importance. In our work, a NiFe2O4/N-BCNT supported magnetic catalyst was prepared by a modified coprecipitation method. The catalyst support alone also showed activity in the synthesis of TDA. Platinum nanoparticles were deposited on the catalyst support surface by a fast, relatively simple, and efficient sonochemical method, resulting in a readily applicable catalytically active system. The prepared catalyst exhibited high activity in hydrogenation tests, which was proved by the exceptionally high DNT conversion (100% for 120 min at 333 K) and TDA yield (99%). Furthermore, the magnetic catalyst can be easily recovered from the reaction medium by the action of an external magnetic field, which can greatly reduce catalyst loss during separation.

Electrospun Nanofiber Mats with Embedded Zinc Oxysulfide for Photoreduction of Nitrobenzene to Aniline under Mild Condition

In this work, electrospun nanofiber embedded with zinc oxysulfide (Zn(O,S)) has been demonstrated as an efficient and robust photocatalyst for hydrogenation of nitrobenzene to aniline under solar light irradiation at mild conditions with methanol as the hole scavenger. The solid solution state of Zn(O,S) in electrospun nanofiber was successfully revealed by high-resolution transmission electron microscopy and X-ray diffraction analyses in which the lattice fringes and diffraction planes located in between those of ZnO and ZnS phases. Moreover, the electrochemical and optical properties of Zn(O,S) embedded in polyethylene oxide (PEO) nanofiber are found to be better than those of ZnO and ZnS indicating more efficient photocatalytic activities as well. The photocatalytic hydrogenation of nitrobenzene to aniline occurred completely within 2 h of the photocatalytic reaction with a reusability of 95% after five consecutive runs. Finally, the mechanism of photocatalytic hydrogenation by Zn(O,S) embedded in the PEO (PZOS) nanofiber involves a total of six electrons (e-) and six protons (H+) to hydrogenate nitrobenzene to nitrosobenzene, phenylhydroxylamine, and aniline.

Preparation of polysubstituted imidazoles using AC-SO3H/[Urea]7[ZnCl2]2 as an efficient catalyst system: a novel method, and α-glucosidase inhibitor activity

Deep eutectic solvents (DESs) act as both an organic solvent and a useful catalyst for organic synthesis reactions, especially the synthesis of heterocyclic compounds containing the element nitrogen. DESs exhibit many important properties namely large liquid fields, biodegradability, outstanding thermal stability, and moderate vapor pressure. Amorphous carbon-bearing sulfonic acid groups (AC-SO₃H) are one of the new-generation solid acids showing strong acid activity. Based on the simultaneous presence of acidic functional groups such as carboxylic acid, phenolic, and sulfonic acid groups, they exhibit many important activities namely strong Brønsted acid, high surface area, high stability, reusability, and recyclability. In this study, AC-SO₃H was made from rice husk via the carbonization and sulfonation processes, and the surface properties and structure were examined using contemporary methods such as FT-IR, P-XRD, TGA, SEM, and EDS. And, [Urea]₇[ZnCl₂]₂ was synthesized from urea and ZnCl₂ with a mole ratio of 7 : 2; the structure is defined using FT-IR and TGA. By combining AC-SO₃H and [Urea]₇[ZnCl₂]₂ we aim to form an effective catalyst/solvent system for the preparation of polysubstituted imidazole derivatives through the multi-component cyclization reaction from nitrobenzenes, benzil, aldehydes, and ammonium acetate. The major products are obtained with high isolation yields above 60%. To assess the catalyst system's activity, the recovery and reusability of the AC-SO₃H/[Urea]₇[ZnCl₂]₂ system were examined with hardly any performance modification. In an effort to create potential enzyme α-glucosidase inhibitors, several novel polysubstituted imidazoles were created. Five of these compounds showed good enzyme α-glucosidase inhibitor activity. The most effective substances were IMI-13, IMI-15, and IMI-20, with IC₅₀ values that were greater than the acarbose at 16.5, 15.8, and 11.6 μM, respectively - the acarbose (IC₅₀, 214.5 μM) as the positive control.

Visible-Light-Driven Porphyrin-Based Bimetallic Metal-Organic Frameworks for Selective Photoreduction of Nitro Compounds under Mild Conditions

Selective reduction of nitroaromatics to the corresponding amines generally requires complex conditions, involving pressurized hydrogen, higher temperatures, or organic acids. In this work, we successfully prepared a series of porphyrin-based MOF photocatalysts (Pd-PMOFs, In-PMOFs, and In/Pd-PMOFs) via a facile solvothermal method for the efficient selective reduction of nitroaromatics to corresponding anilines with deionized water as the hydrogen donor. Being a new structured material (monoclinic, C₅₂H₄₀InN₆O₈Pd), on account of the abundant pore channels, strong light absorption capability, well-matched bandgap, as well as the coordination of indium ions and palladium ions, In/Pd-MOFs have excellent migration efficiency of photo-induced electrons and holes. Specifically, the In/Pd-PMOF photocatalyst manifested superior conversion (100%) and selectivity (≥80%) toward the screened nitro compounds under mild conditions. This work avoids the use of strong reductants, organic acids, and pressurized hydrogen gas as hydrogen sources, providing a promising concept for developing green catalytic systems.

Asymmetric Activation of the Nitro Group over a Ag/Graphene Heterointerface to Boost Highly Selective Electrocatalytic Reduction of Nitrobenzene

The electrocatalytic reduction of nitrobenzene to aniline normally faces high overpotential and poor selectivity because of its six-electron redox nature. Herein, a Ag nanoparticles/laser-induced-graphene (LIG) heterointerface was fabricated on polyimide films and employed as an electrode material for an efficient nitrobenzene reduction reaction (NBRR) via a one-step laser direct writing technology. The first-principles calculations reveal that Ag/LIG shows the lowest activation barriers for the NBRR, which could be attributed to the optimum adsorption of the H atom realized by the appropriate interaction between Ag/LIG heterointerfaces and nitrobenzene. As a result, the overpotential of the NBRR is reduced by 217 mV after silver loading, and Ag/LIG shows a high aniline selectivity of 93%. Furthermore, an electrochemical reduction of nitrobenzene in tandem with an electrochemical oxidative polymerization of aniline was designed to serve as an alternative method to remove nitrobenzene from the aqueous solution. This strategy highlights the significance of heterointerfaces for efficient electrocatalysts, which may stimulate the development of novel electrocatalysts to boost the electrocatalytic activity.

Comparison of Catalysts with MIRA21 Model in Heterogeneous Catalytic Hydrogenation of Aromatic Nitro Compounds

The vast majority of research and development activities begins with a detailed literature search to explore the current state-of-the-art. However, this search becomes increasingly difficult as we go into the information revolution of 21st century. The aim of the work is to establish a functional and practical mathematical model of catalyst characterization and exact comparison of catalysts. This work outlines the operation of the MIskolc RAnking 21 (MIRA21) model through the reaction of nitrobenzene catalytic hydrogenation to aniline. A total of 154 catalysts from 45 research articles were selected, studied, characterized, ranked, and classified based on four classes of descriptors: catalyst performance, reaction conditions, catalyst conditions, and sustainability parameters. MIRA21 is able to increase the comparability of different types of catalysts and support catalyst development. According to the model, 8% of catalysts received D1 (top 10%) classification. This ranking model is able to show the most effective catalyst systems that are suitable for the production of aniline.

Modifying electron injection kinetics for selective photoreduction of nitroarenes into cyclic and asymmetric azo compounds

Modifying the reactivity of substrates by encapsulation is essential for microenvironment catalysts. Herein, we report an alternative strategy that modifies the entry behaviour of reactants into the microenvironment and substrate inclusion thermodynamics related to the capsule to control the electron injection kinetics and the selectivity of products from the nitroarenes photoreduction. The strategy includes the orchestration of capsule openings to control the electron injection kinetics of electron donors, and the capsule’s pocket to encapsulate more than one nitroarene molecules, facilitating a condensation reaction between the in situ formed azanol and nitroso species to produce azo product. The conceptual microenvironment catalyst endows selective conversion of asymmetric azo products from different nitroarenes, wherein, the estimated diameter and inclusion Gibbs free energy of substrates are used to control and predict the selectivity of products. Inhibition experiments confirm a typical enzymatic conversion, paving a new avenue for rational design of photocatalysts toward green chemistry.

Reductive Alkylation of Azides and Nitroarenes with Alcohols: A Selective Route to Mono- and Dialkylated Amines

Herein, we demonstrated an efficient protocol for reductive alkylation of azides/nitro compounds via a borrowing hydrogen (BH) method. By following this protocol, selective mono- and dialkylated amines were obtained under mild and solvent-free conditions. A series of control experiments and deuterium-labeling experiments were performed to understand this catalytic process. Mechanistic studies suggested that the Ir(III)-H was the active intermediate in this reaction. KIE study revealed that the breaking of the C-H bond of alcohol might be the rate-limiting step. Notably, this solvent-free strategy disclosed a high TON of around 5600. Based on kinetic studies and control experiments, a metal-ligand cooperative mechanism was proposed.

Computational Screening of First-Row Transition-Metal Based Alloy Catalysts-Ligand Induced N2 Reduction Reaction Selectivity

Large-scale ammonia production through sustainable strategies from naturally abundant N₂ under ambient conditions represents a major challenge from a future perspective. Ammonia is one of the promising carbon-free alternative energy carriers. The high energy required for N≡N bond dissociation during the Haber-Bosch process demands extreme reaction conditions. This problem could be circumvented by tuning Fe catalyst composition with the help of an induced ligand effect on the surface. In this work, we utilized density functional theory calculations on the Fe(110) surface alloyed with first-row transition-metal (TM) series (Fe-TM) to understand the catalytic activity that facilitates the electrochemical nitrogen reduction reaction (NRR). We also calculated the selectivity against the competitive hydrogen evolution reaction (HER) under electrochemical conditions. The calculated results are compared with those from earlier reports on the periodic Fe(110) and Fe(111) surfaces, and also on the (110) surface of the Fe₈₅ nanocluster. Surface alloying with late TMs (Co, Ni, Cu) shows an improved NRR activity, whereas the low exchange current density observed for Fe-Co indicates less HER activity among them. Considering various governing factors, Fe-based alloys with Co (Fe-Co) showed enhanced overall performance compared to the periodic surface as well as other pure iron-based structures previously reported. Therefore, the iron-alloy based structured catalysts may also provide more opportunities in the future for enhancing NRR performance via electrochemical reduction pathways.

Single non-noble metal atom doped C2N catalysts for chemoselective hydrogenation of 3-nitrostyrene

Improving the reaction selectivity and activity for challenging substrates such as nitroaromatics bearing two reducible functional groups is important in industry, yet remains a great challenge using traditional metal nanoparticle based catalysts. In this study, single metal atom doped M-C₂N catalysts were theoretically screened for selective hydrogenation of 3-nitrostyrene to 3-vinylaniline with H₂ as the H-source. Among 20 M-C₂N catalysts, the non-noble Mn-C₂N catalyst was found to have excellent reaction selectivity. Importantly, due to the solid frustrated Lewis pair sites in the pores of Mn-C₂N, a low H₂ activation energy is achieved on high-spin Mn-C₂N and the rate-determining step for the hydrogenation reactions is the H diffusion from the metal site to the N site. The unraveled mechanism of the hydrogenation of 3-nitrostyrene using Mn-C₂N enriches the applications of Mn based catalysts and demonstrates its excellent properties for catalyzing the challenging hydrogenation reaction of substrates with two reducible functional groups.

Combined Spectroscopic and Computational Study of Nitrobenzene Activation on Non-Noble Metals-Based Mono- and Bimetallic Catalysts

In this paper, substituted anilines are industrially obtained by direct hydrogenation of nitroaromatic compounds with molecular H₂ using metals as catalysts. Previous theoretical studies proposed that the mechanism of the reaction depends on the nature of the metal used as a catalyst, and that rationally designed bimetallic materials might show improved catalytic performance. Herein, we present IR spectroscopic studies of nitrobenzene interactions with monometallic Ni/SiO₂, Cu/SiO₂ and Pd/SiO_2, and with bimetallic CuNi/SiO₂ and CuPd/SiO₂ catalysts, both in the absence and presence of H₂, combined with density functional theory (DFT) calculations on selected bimetallic NiCu(111) and PdCu(111) models. The results obtained experimentally confirm that the reaction mechanism on non-noble metals such as Ni proceeds through N-O bond dissociation, generating nitrosobenzene intermediates, while, on noble metals, such as Pd, H-attack is necessary to activate the NO bond. Moreover, a bimetallic CuPd/SiO₂ catalyst with a Pd enriched surface is prepared that exhibits an enhanced H₂ dissociation ability and a particular reactivity at the boundary between the two metals.

Mycoremediation and toxicity assessment of textile effluent pertaining to its possible correlation with COD

Globally, textile industries are one of the major sectors releasing dye pollutants. This is the first report on the positive correlation between toxicity and chemical oxygen demand (COD) of textile effluent along with the proposed pathway for enzymatic degradation of acid orange 10 using Geotrichum candidum within a very short stretch of time (18 h). Removal efficiency of this mycoremedial approach after 18 h in terms of chemical oxygen demand, biological oxygen demand, total suspended solids, salinity, color and dye concentration in the treated effluent reached to 98.5%, 56.3%,73.2%, 64%, 89% and 87% respectively. Also there was a decrease in pH of the treated effluent. FTIR analysis of the treated effluent confirmed biodegradation. The LCMS analysis showed the degradation of acid orange 10, which was confirmed by the formation of two biodegradation products, 7-oxo-8-iminonapthalene-1,3-disulfonate and nitrosobenzene, which subsequently undergoes stepwise hydrogenation and dehydration to form aniline via phenyl hydroxyl amine as intermediate. The X-ray diffraction studies showed that heavy metal content in the treated effluent has reduced along with decrease in % crystallinity, indicating biodegradation. The connection between toxicity and COD was also inveterated using Pearson's correlation coefficient. Further the toxicological studies indicated the toxicity of raw textile effluent and relatively lower toxic nature of metabolites generated after biodegradation by G. candidum.

Ab Initio Studies of Bimetallic-Doped {0001} Hematite Surface for Enhanced Photoelectrochemical Water Splitting

First-principles calculations based on density functional theory (DFT) were carried out to study the energetic stability and electronic properties of a bimetallic-doped α-Fe2O3 photoanode surface with (Zn, Ti) and (Zn, Zr) pairs for enhanced PEC water splitting. The doped systems showed negative formation energies under both O-rich and Fe-rich conditions which make them thermodynamically stable and possible to be synthesised. It is found that in a bimetallic (Zn, Ti)-doped system, at a doping concentration of 4.20% of Ti, the bandgap decreases from 2.1 eV to 1.80 eV without the formation of impurity states in the bandgap. This is favourable for increased photon absorption and efficient movement of charges from the valance band maximum (VBM) to the conduction band minimum (CBM). In addition, the CBM becomes wavy and delocalised, suggesting a decrease in the charge carrier mass, enabling electron–holes to successfully diffuse to the surface, where they are needed for water oxidation. Interestingly, with single doping of Zr at the third layer (L3) of Fe atoms of the {0001} α-Fe2O3 surface, impurity levels do not appear in the bandgap, at both concentrations of 2.10% and 4.20%. Furthermore, at 2.10% doping concentration of α-Fe2O3 with Zr, CBM becomes delocalised, suggesting improved carrier mobility, while the bandgap is altered from 2.1 eV to 1.73 eV, allowing more light absorption in the visible region. Moreover, the photocatalytic activities of Zr-doped hematite could be improved further by codoping it with Zn because Zr is capable of increasing the conductivity of hematite by the substitution of Fe3+ with Zr4+, while Zn can foster the surface reaction and reduce quick recombination of the electron–hole pairs.

Production of copper nanoparticles exhibiting various morphologies via pulsed laser ablation in different solvents and their catalytic activity for reduction of toxic nitroaromatic compounds

Comparative experiments were conducted to determine the effects of various solvents (i.e., deionized water, methanol, ethanol, 1-propanol, butanol, ethylene glycol, hexane, and acetonitrile) on the final compositions, morphologies, and catalytic activities of copper-based nanoparticles (NPs). The NPs were effectively synthesized by pulsed laser ablation (PLA) using a copper plate as the target. The obtained copper NPs were characterized utilizing various analytical techniques. It was established that the developed methodology allows for the production of NPs with different morphologies and compositions in a safe and simple manner. When laser ablation of a solid copper plate was performed in acetonitrile, the formation of copper(I) cyanide cubes was observed. On the other hand, in deionized water and methanol, spherical and rod-like particles of copper(I) and copper(II) oxide were detected, respectively. The catalytic activity of the prepared copper NPs in the reduction of aromatic nitro compounds, such as 4-nitrophenol and nitrobenzene, was also evaluated. A high k value was determined for the reduction over the copper(II) oxide NPs produced in methanol. Moreover, particles with graphitic carbon (GC) layers exhibited superior catalytic performance in the reduction of a hydrophobic substance, i.e., nitrobenzene, over the reduction of 4-nitrophenol. The enhanced catalytic activity of this catalyst may be due its unique surface morphology and the synergistic effects between the copper nanostructure and the GC layer. Lastly, a detailed reduction pathway mechanism for the catalytic reduction of 4-nitrophenol and nitrobenzene has been proposed.

Hydrogenation of substituted nitroaromatics on non-noble metal catalysts: mechanistic insights to improve selectivity

The mechanism of nitrobenzene hydrogenation on non-noble metals such as Ni is different from that previously reported for noble metals like Pt. The newly proposed pathway involves the initial dissociation of the two N-O bonds of nitrobenzene (Ph-NO₂→ Ph-NO → Ph-N), leading to partial oxidation of the catalyst surface, followed by two successive hydrogenation steps (Ph-N → Ph-NH → Ph-NH₂) that finally produce the functionalized aniline. Due to the oxophilic nature of non-noble metals like Ni, Co or Cu, the hydrogenation of the Ph-N intermediate and the removal of O in the form of water become the most energy demanding steps of the process. The strength of the interaction of O, H and N with different metals, and the preferential mode of adsorption of nitroarenes on clean and partially oxidized systems obtained from DFT calculations, are now used to propose an efficient non-noble metal catalyst that optimizes activity and selectivity.

Bimetallic Co/Zn zeolitic imidazolate framework ZIF-67 supported Cu nanoparticles: An excellent catalyst for reduction of synthetic dyes and nitroarenes

In this study, a sub-class of microporous crystalline metal organic frameworks (MOFs) with zeolite-like configurations, i.e., zeolitic imidazolate frameworks of single node ZIF-67 and binary nodes ZIF-Co/Zn are used as the supports to develop Cu nanoparticles based nanocatalysts. Their catalytic activities are comparatively evaluated where Cu(x)@ZIF-Co/Zn exhibits better performances than Cu(x)@ZIF-67 in the reduction of synthetic dyes and nitroarenes. For instance, the Cu(0.25)@ZIF-Co/Zn catalyst shows an excellent reaction rate of 2.088 × 10^-2 s^-1 and an outstanding activity of 104.4 s^-1g_cat^-1 for the reduction of methyl orange. The same catalyst also performs an exceptional catalytic activity in the hydrogenation of p-nitrophenol to p-aminophenol with the activity of 216.5 s^-1g_cat^-1. A synergistic role of unique electronic properties rising from the direct contact of Cu NPs with the bimetallic nodes ZIF-Co/Zn, higher surface area of support, appropriate Cu loading and maintainable microporous frameworks with higher thermal and hydrolytic stability collectively enhances the catalytic activity of Cu(x)@ZIF-Co/Zn. Moreover, this catalyst shows excellent stability and recyclability, which can retain high conversion after reuse for 10 cycles.

Ultra-small FeS2 nanoparticles for highly efficient chemoselective transfer hydrogenation of nitroarenes

Ultra-small FeS2 nanoparticles are shown to give superior catalytic performance in hydrogen transfer reactions for the synthesis of substituted anilines.

A Qualitative Numerical Study on Catalytic Hydrogenation of Nitrobenzene in Gas-Liquid Taylor Flow with Detailed Reaction Mechanism

While the number of computational studies considering two-phase flows in microfluidic systems with or without mass transfer is increasing, numerical studies incorporating chemical reactions are still rare. This study aims to simulate the catalytic hydrogenation of nitrobenzene in gas-liquid Taylor flow by combining interface-resolving numerical simulations of two-phase flow and mass transfer by a volume-of-fluid method with detailed modeling of the heterogeneous chemical reaction by software package DETCHEMTM. Practically relevant physical properties are utilized for hydrodynamic and mass transfer simulations in combination with a preliminary reaction mechanism based on density functional theory. Simulations of mass transfer are conducted using a predetermined velocity field and Taylor bubble shape. At the beginning of the simulation when liquid nitrobenzene is not saturated by hydrogen, axial profiles of surface species concentrations and reaction rates show local variations. As hydrogen dissolves in nitrobenzene, the concentration profiles of surface species at the wall become uniform, eventually reaching an equilibrium state. Neglecting the local variation in a short initial period will allow further simplification of modeling surface reactions within a Taylor flow.

Highly Selective Synthesis of Hydrazoarenes from Nitroarenes via Polystyrene-Supported Au-Nanoparticle-Catalyzed Reduction: Application to Azoarenes, Aminoarenes, and 4,4'-Diaminobiaryls

A selective synthesis of hydrazoarene from nitroarene and its application are reported. Using polystyrene (PS) resins as solid supports for Au nanoparticles (AuNPs), polystyrene-supported Au nanoparticles (AuNPs@PS) were synthesized and characterized. In the presence of AuNPs@PS (1.0 mol %) as a catalyst, nitroarenes afforded corresponding hydrazoarenes (up to 99%) with high selectivity (up to 100%) under mild reaction conditions (NaBH₄, 50% aq. EtOH, and room temperature). Depending on the reaction conditions (the amount of NaBH₄, the substituent of nitroarenes, and the sequential addition of HCl), nitroarenes were converted to corresponding azoarenes (up to 95%), aminoarenes (up to 99%), and 4,4'-diaminobiaryls (up to 99%). Our easily recyclable catalytic system using a solid-phase reaction vessel provides an attractive synthetic method in an eco-friendly and sustainable manner.

Effect of Fe, Co and Ni promoters on MoS2 based catalysts for chemoselective hydrogenation of nitroarenes

The effect of Fe, Co and Ni promoters on supported MoS₂ catalysts for hydrogenation of nitroarenes were systematically investigated via experiment, characterization and DFT calculation. It was found that the addition of promoters remarkably improved the reaction activity in a sequence of Ni > Co > Fe > Mo. Meanwhile Ni promoted catalyst with the best performance showed good recyclability and chemoselectivity for a wide substrate scope. The characterization results revealed that the addition of promoters decreased the interaction between Mo and support and facilitated the reductive sulfidation of Mo species to produce more coordinated unsaturated sites (CUS). DFT calculations showed that the addition of promoters increased the formation of CUS, and enhanced the adsorption of hydrogen. The influence degree of promoters followed the sequence Ni > Co > Fe > Mo, which was consistent with those of the activities. Nitrobenzene hydrogenation and hydrogen activation occurred at the S and Mo edge, respectively. The adsorbed hydrogen diffused from the Mo edge to the S edge to participate in the hydrogenation reaction. Mechanism investigation showed that the main reason for increased activity by the addition of promoters was the increase of amounts of CUS and the secondary reason was the augmentation of intrinsic activity of CUS. The present studies give a new understanding for promoter modified MoS₂ catalysts applied for hydrogenation of nitroarenes.

The addition of promoters remarkably improved the activity for hydrogenation of nitroarenes in a sequence of Ni > Co > Fe > Mo and the amount of CUS active center was supposed to be the main reason to influence the reaction activity.

Ultrafine bimetallic Ag-doped Ni nanoparticles embedded in cage-type mesoporous silica SBA-16 as superior catalysts for conversion of toxic nitroaromatic compounds

Highly active Ag-doped Ni nanoparticles are successfully fabricated within carboxylic acid (-COOH) functionalized mesoporous silica SBA-16 by a facile wet incipient technique for catalytic conversion of toxic nitroaromatics. The -COOH groups on SBA-16 play a crucial role by enhancing the electrostatic interactions with Ag(I)/Ni(II) cations, that control the crystal growth during the thermal reduction. Systematic characterizations of SBA-16C and Ag_x%Ni@SBA-16C are performed by different techniques including solid state ¹³C and ²⁹Si nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), N₂ sorption, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and superconducting quantum interference device (SQUID). The highly dispersed ultrafine Ag-doped Ni NPs (∼3 nm) are well-confined within SBA-16C and exhibit magnetic properties that are extremely beneficial for recycling. The bimetallic Ag_2.4%Ni@SBA-16C shows exceptionally high catalytic activity during catalytic conversion of toxic nitroaromatics to environmentally friendly amino-aromatics. The enhanced catalytic activity could be ascribed to the combined effects of unique electronic properties, synergistic effects of Ag-doped Ni, ultra-small size, metal loading, and favorable textural properties. These magnetically separable nanocatalysts show excellent durability.

The composition of transformation products of 2,4,6-trinitrobenzoic acid in the aqueous-phase hydrogenation over Pd/C catalysts

Due to a detailed analysis of NMR spectra of the reaction solutions with different composition obtained by the aqueous-phase catalytic (Pd/C) hydrogenation of 2,4,6-trinitrobenzoic acid, the intermediate compounds were identified and a more substantiated mechanism was proposed for the formation of the main reaction products-1,3,5-triaminobenzene and cyclohexane-1,3,5-trione trioxime. The condensation of the 1,3,5-triaminobenzene molecules produced by a complete hydrogenation of 2,4,6-trinitrobenzoic acid was shown to result in the formation of a paramagnetic heterocyclic compound.

Biomass-derived carbon-supported Ni catalyst: an effective heterogeneous non-noble metal catalyst for the hydrogenation of nitro compounds

The biomass-derived carbon material supported Ni catalysts (Ni/C) demonstrated a high catalytic activity for the hydrogenation of nitro compounds into primary amines at room temperature.

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

The reduction of nitro compounds to the corresponding amines is one of the most utilized catalytic processes in the fine and bulk chemical industry. The latest development of catalysts with cheap metals like Fe, Co, Ni, and Cu has led to their tremendous achievements over the last years prompting their greater application as "standard" catalysts. In this review, we will comprehensively discuss the use of homogeneous and heterogeneous catalysts based on non-noble 3d-metals for the reduction of nitro compounds using various reductants. The different systems will be revised considering both the catalytic performances and synthetic aspects highlighting also their advantages and disadvantages.

Catalytic Hydrogenation of p-Chloronitrobenzene to p-Chloroaniline Mediated by γ-Mo2N

Promoting the production of industrially important aromatic chloroamines over transition-metal nitrides catalysts has emerged as a prominent theme in catalysis. This contribution provides an insight into the reduction mechanism of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CAN) over the γ-Mo₂N(111) surface by means of density functional theory calculations. The adsorption energies of various molecularly adsorbed modes of p-CNB were computed. Our findings display that, p-CNB prefers to be adsorbed over two distinct adsorption sites, namely, Mo-hollow face-centered cubic (fcc) and N-hollow hexagonal close-packed (hcp) sites with adsorption energies of -32.1 and -38.5 kcal/mol, respectively. We establish that the activation of nitro group proceeds through direct pathway along with formation of several reaction intermediates. Most of these intermediaries reside in a significant well-depth in reference to the entrance channel. Central to the constructed mechanism is H-transfer steps from fcc and hcp hollow sites to the NO/-NH groups through modest reaction barriers. Our computed rate constant for the conversion of p-CNB correlates very well with the experimental finding (0.018 versus 0.033 s^-1 at ∼500 K). Plotted species profiles via a simplified kinetics model confirms the experimentally reported high selectivity toward the formation of p-CAN at relatively low temperatures. It is hoped that thermokinetics parameters and mechanistic pathways provided herein will afford a molecular level understanding for γ-Mo₂N-mediated conversion of halogenated nitrobenzenes into their corresponding nitroanilines; a process that entails significant industrial applications.

Pt Single Atoms Embedded in the Surface of Ni Nanocrystals as Highly Active Catalysts for Selective Hydrogenation of Nitro Compounds

Single-atom catalysts exhibit high selectivity in hydrogenation due to their isolated active sites, which ensure uniform adsorption configurations of substrate molecules. Compared with the achievement in catalytic selectivity, there is still a long way to go in exploiting the catalytic activity of single-atom catalysts. Herein, we developed highly active and selective catalysts in selective hydrogenation by embedding Pt single atoms in the surface of Ni nanocrystals (denoted as Pt₁/Ni nanocrystals). During the hydrogenation of 3-nitrostyrene, the TOF numbers based on surface Pt atoms of Pt₁/Ni nanocrystals reached ∼1800 h^-1 under 3 atm of H₂ at 40 °C, much higher than that of Pt single atoms supported on active carbon, TiO₂, SiO₂, and ZSM-5. Mechanistic studies reveal that the remarkable activity of Pt₁/Ni nanocrystals derived from sufficient hydrogen supply because of spontaneous dissociation of H₂ on both Pt and Ni atoms as well as facile diffusion of H atoms on Pt₁/Ni nanocrystals. Moreover, the ensemble composed of the Pt single atom and nearby Ni atoms in Pt₁/Ni nanocrystals leads to the adsorption configuration of 3-nitrostyrene favorable for the activation of nitro groups, accounting for the high selectivity for 3-vinylaniline.

Single-site catalyst promoters accelerate metal-catalyzed nitroarene hydrogenation

Atomically dispersed supported metal catalysts are drawing wide attention because of the opportunities they offer for new catalytic properties combined with efficient use of the metals. We extend this class of materials to catalysts that incorporate atomically dispersed metal atoms as promoters. The catalysts are used for the challenging nitroarene hydrogenation and found to have both high activity and selectivity. The promoters are single-site Sn on TiO₂ supports that incorporate metal nanoparticle catalysts. Represented as M/Sn-TiO₂ (M = Au, Ru, Pt, Ni), these catalysts decidedly outperform the unpromoted supported metals, even for hydrogenation of nitroarenes substituted with various reducible groups. The high activity and selectivity of these catalysts result from the creation of oxygen vacancies on the TiO₂ surface by single-site Sn, which leads to efficient, selective activation of the nitro group coupled with a reaction involving hydrogen atoms activated on metal nanoparticles.

Understanding of the structures and roles of catalyst promoters markedly lags behind the understanding of the structures and roles of catalytic sites. Here, the authors address this challenge by incorporating a single-site promoter—tin—on a TiO₂ surface to enhance the catalytic activity of various metals on the TiO₂ in selective hydrogenation of nitroarenes.

Synthesis of Mesoporous γ-Alumina-Supported Co-Based Catalysts and Their Catalytic Performance for Chemoselective Reduction of Nitroarenes

Mesoporous γ-alumina (γ-MA)-supported cobalt oxides (Co₃O₄) with large surface areas and narrow pore size distributions were first prepared through one-pot hydrolysis of metal nitrates. The obtained Co₃O₄/γ-MA materials were impregnated with a water-ethanol solution of 1,10-phenanthroline, followed by treatment at 700 °C in N₂ atmosphere, generating Co-NC/γ-MA catalysts containing N-doped graphitic carbon (NC). The Co-NC/γ-MA catalysts maintained the mesoporous structure of γ-MA, and Co₃O₄ was reduced to metallic Co nanoparticles highly dispersed in the γ-MA frameworks. Metallic Co species had a strong interaction with NC in the matrices, avoiding the surface oxidation of Co particles. The Co-NC/γ-MA catalysts exhibited superior catalytic activity and quantitatively reduced a variety of functionalized nitroarenes to the corresponding arylamines with hydrazine hydrate in ethanol at near room temperature, affording yields of >99%. The recycling test of 2-chloronitrobenzene as a model reaction showed no detectable change in catalyst performance after 10 cycle reactions.

High performance of a cobalt-nitrogen complex for the reduction and reductive coupling of nitro compounds into amines and their derivatives

Replacement of precious noble metal catalysts with low-cost, non-noble heterogeneous catalysts for chemoselective reduction and reductive coupling of nitro compounds holds tremendous promise for the clean synthesis of nitrogen-containing chemicals. We report a robust cobalt-nitrogen/carbon (Co-N _x /C-800-AT) catalyst for the reduction and reductive coupling of nitro compounds into amines and their derivates. The Co-N _x /C-800-AT catalyst was prepared by the pyrolysis of cobalt phthalocyanine-silica colloid composites and the subsequent removal of silica template and cobalt nanoparticles. The Co-N _x /C-800-AT catalyst showed extremely high activity, chemoselectivity, and stability toward the reduction of nitro compounds with H₂, affording full conversion and >97% selectivity in water after 1.5 hours at 110°C and under a H₂ pressure of 3.5 bar for all cases. The hydrogenation of nitrobenzene over the Co-N _x /C-800-AT catalyst can even be smoothly performed under very mild conditions (40°C and a H₂ pressure of 1 bar) with an aniline yield of 98.7%. Moreover, the Co-N _x /C-800-AT catalyst has high activity toward the transfer hydrogenation of nitrobenzene into aniline and the reductive coupling of nitrobenzene into other derivates with high yields. These processes were carried out in an environmentally friendly manner without base and ligands.

Catalytically active designer crown-jewel Pd-based nanostructures encapsulated in metal-organic frameworks

A series of crown-jewel Pd-based bimetallic nanostructures with tunable composition are fabricated inside the pores of an MOF via a hydride-induced-reduction strategy, exhibiting high activity and stability in the hydrogenation of nitrobenzene.