Hydrogenation Of Nitrobenzene Research Articles

Tuning product selectivity in nitrobenzene reduction over a single Bi2MoO6 photocatalyst in one pot: Mechanisms and roles of reaction compositions

Poor product selectivity of metal oxide photocatalysts is one of crucial issues limiting their application in photocatalytic organic synthesis particularly when multiple parallel reactions as well as several intermediates and products are involved, as in the reduction of nitrobenzene (NB) in this present study. Accordingly, catalyst modification is often needed. Herein, we first demonstrate that without catalyst modification it is feasible to control product selectivity over a single bismuth molybdate photocatalyst to selectively prepare three different valuable compounds including aniline (AN), azobenzene (AZO) and azoxybenzene (AZX) with high efficacy. Two widely used bismuth molybdate photocatalysts, namely Bi2MoO6 and Bi4MoO9, were studied and compared. Bi2MoO6 offers better visible-light-driven photocatalytic performance than Bi4MoO9 partly due to its narrow band gap energy and efficient charge carrier separation and transfer as evidenced from UV–vis DRS, EIS, and transient photocurrent studies. The roles of hydrazine hydrate, alcohol solvent, and KOH additive on the transfer hydrogenation of NB were examined and their concentrations were optimized to solely obtain the three different products with excellent selectivity (>98%). Based on UV–vis DRS and Mott-Schottky analysis, the band energy level of Bi2MoO6 and plausible reactions at solid–liquid interface are proposed. The capability to control product selectivity over a single photocatalyst in one pot demonstrated in this work would make the process more practical especially for continuous flow photochemical systems.

Water acting as a catalytic promoter for electron-proton transfer in the Pt single atom catalyzed environmental reduction reactions

Water, which is the host of life, introduces many unusual features into the kinetics and energetics of biological reaction systems catalyzed by enzymes. Single atom catalyst has great potential to mimic biological enzymes in regard to special catalytic sites and high efficiency. Here we report a significant promotion by H2O in the environmental reduction of nitrobenzene on an environmentally friendly humic acid supported Pt single atom catalyst. No nitrobenzene conversion took place when only organic solvents were used while high activity of the catalyst was observed in aqueous mixtures (turnover frequency is as high as 1883 h−1). Experiments and density functional theory calculation show that H2O greatly decreased the energy barrier by enabling a biomimetic electron-proton transfer for the hydrogenation process even on single atom Pt catalyst, and a new reaction pathway with phenyl-λ1-azane as intermediate in the direct hydrogenation of nitrobenzene is proposed.

A novel process for the synthesis of p‐aminophenol by transfer hydrogenation of nitrobenzene using formic acid as hydrogen source

Abstractp‐Aminophenol (PAP) was synthesized via the transfer hydrogenation of nitrobenzene (NB) over a Pd/AC + SO42−/ZrO2 catalyst using formic acid as the hydrogen source. Pd loading had an obvious effect on the reaction, with an optimal loading of 7 wt.%. The average Pd crystallite size was 3–4 nm, and both Pd0 and Pd2+ species were present on the catalyst surface. The relative proportions of Pd0 and Pd2+ affected the synthesis of PAP, with higher Pd2+ concentrations increasing the PAP selectivity. The reaction conditions for PAP synthesis were optimized, and an NB conversion of 69.6% with 38.1% PAP selectivity was obtained. After the same catalyst sample was used four times, the NB conversion decreased from 69.6% to 61.3%, and PAP selectivity decreased from 34.7% to 21.5%. These changes were attributed to the loss of Pd and S from the catalyst.

Development of High-Efficiency, Magnetically Separable Palladium-Decorated Manganese-Ferrite Catalyst for Nitrobenzene Hydrogenation.

Aniline (AN) is one of the most important compounds in the chemical industry and is prepared by the catalytic hydrogenation of nitrobenzene (NB). The development of novel, multifunctional catalysts which are easily recoverable from the reaction mixture is, therefore, of paramount importance. Compared to conventional filtration, magnetic separation is favored because it is cheaper and more facile. For satisfying these requirements, we developed manganese ferrite (MnFe2O4)–supported, magnetically separable palladium catalysts with high catalytic activity in the hydrogenation of nitrobenzene to aniline. In addition to high NB conversion and AN yield, remarkable aniline selectivity (above 96 n/n%) was achieved. Surprisingly, the magnetic support alone also shows moderate catalytic activity even without noble metals, and thus, up to 94 n/n% nitrobenzene conversion, along with 47 n/n% aniline yield, are attainable. After adding palladium nanoparticles to the support, the combined catalytic activity of the two nanomaterials yielded a fast, efficient, and highly selective catalyst. During the test of the Pd/MnFe2O4 catalyst in NB hydrogenation, no by-products were detected, and consequently, above 96 n/n% aniline yield and 96 n/n% selectivity were achieved. The activity of the Pd/MnFe2O4 catalyst was not particularly sensitive to the hydrogenation temperature, and reuse tests indicate its applicability in at least four cycles without regeneration. The remarkable catalytic activity and other favorable properties can make our catalyst potentially applicable to both NB hydrogenation and other similar or slightly different reactions.

Palladium Decorated N-Doped Carbon Foam as a Highly Active and Selective Catalyst for Nitrobenzene Hydrogenation.

Carbon foam was synthesized by the carbonization of 4-nitroaniline. The reaction is an alternative of the well-known “carbon snake” (or sugar snake) demonstration experiment, which leads to the formation of nitrogen-doped carbon foils due to its nitrogen content. The synthesized carbon foils were grinded to achieve an efficient catalyst support. Palladium nanoparticles were deposited onto the surface of the support, which showed continuous distribution. The prepared Pd nanoparticle decorated carbon foils showed high catalytic activity in nitrobenzene hydrogenation. By applying the designed catalyst, total nitrobenzene conversion, a 99.1 n/n% aniline yield, and an exceptionally high selectivity (99.8 n/n%) were reached. Furthermore, the catalyst remained active during the reuse tests (four cycles) even without regeneration.

Strong electronic interaction of indium oxide with palladium single atoms induced by quenching toward enhanced hydrogenation of nitrobenzene

The realization of efficient and fully controllable synthesis of single atom catalysts is an exciting frontier, yet still challenging in the modern catalysis field. Here we describe a straightforward high-temperature quenching approach to precisely construct isolated palladium atoms supported over cubic indium oxide, with individual palladium atoms coordinated with four neighboring oxygen atoms. This palladium catalyst achieves exceptional catalytic efficiency in the selective hydrogenation of nitrobenzene to aniline, with more than 99% chemoselectivity under almost 100% conversion. Moreover, it delivers excellent recyclability, anti-CO poisoning ability, storage stability, and substrate tolerance. DFT calculations further reveal that the high catalytic activity stems from the optimized electronic structure and the charge states of palladium atoms in the defect-containing indium oxide. Our findings provide an effective approach to engineering single atom catalysts at the atomic level and open the door to a wide variety of catalytic reactions.

Glycerol as an excellent hydrogen and electron source for photocatalytic hydrogenation of nitrobenzene in water

The development of a new method for effective utilization of glycerol dissolved in water is needed. In this study, glycerol was used not as an energy source and a starting compound but as an electron and hydrogen source for photocatalytic hydrogenation of nitrobenzene in an aqueous suspension of TiO2 under various conditions. The function of glycerol as an electron and hydrogen source was compared with that of other C3-alcohols and glycols. The results showed that glycerol works most efficiently as an electron and hydrogen source and that electrons extracted from glycerol are directly used for the hydrogenation without formation of other products such as H2. The photocatalytic hydrogenation was also examined under solar light with and without stirring. Important factors for the electron and hydrogen source in the photocatalytic reaction in an aqueous medium are discussed on the basis of the results.

Catalytic transfer hydrogenation of nitrobenzene over Ti3C2/Pd nanohybrids boosted by electronic modification and hydrogen evolution inhibition

Catalytic transfer hydrogenation (CTH) with formic acid attracts much interest in catalysis, but the sluggish H* production and undesirable H2 evolution reaction (HER) limit its practical applications. Herein we anchored Pd nanoparticles (NPs) on layered Ti3C2 MXene for efficient and selective CTH of nitrobenzene in the presence of formic acid. Some electrons in Pd NPs transferred to Ti3C2 MXene upon formation of Ti3C2/Pd nanohybrids, as confirmed by XPS and DFT simulations. The electron transfer changed Pd valance electron configuration from 4d10 to 4d10-x. Such electron-deficient Pd NPs tuned reaction pathway and promoted formic acid dissociation, both of which favored the production of active H* atoms, i.e., the exact reductant for CTH. Compared with Pd NPs, Ti3C2/Pd showed stronger adsorption of H* and therefore inhibited the occurrence of HER (2H*→H2). Owing to favorable H* production and HER inhibition, Ti3C2/Pd (15 wt% Pd) showed enhanced nitrobenzene CTH performance with turnover frequency of 351.7 h−1 and 99% aniline selectivity, outperforming most of current catalysts. Our work might inspire designing more advanced CTH catalysts by tuning their valance electron configurations with 2D MXene materials.

Catalytic reaction coupling of propane dehydrogenation with nitrobenzene hydrogenation over Pt/Al2O3

Reaction coupling between propane dehydrogenation and nitrobenzene hydrogenation over a commercial Pt/Al2O3 catalyst is presented. The effects of coupling, use of the catalyst, and reaction temperature were studied using a fixed-bed reactor. The coupling of the two reactions drastically increased propane and nitrobenzene conversions even without the use of the catalyst. The use of Pt/Al2O3 further increased the conversions and the selectivity towards propylene and nitrobenzene hydrogenation products. Higher reaction temperatures favored the selectivity towards pyrolysis products. Reaction pathways are sketched to explain our experimental findings.

Phosphorus-Doped Activated Coconut Shell Carbon-Anchored Highly Dispersed Pt for the Chemoselective Hydrogenation of Nitrobenzene to p-Aminophenol.

Highly dispersed Pt nanoparticles (∼2.5 nm) on phosphorus-doped activated coconut shell carbon (Pt/P-ACC) were synthesized by a two-step impregnation route. Pt/P-ACC showed a high activity, chemoselectivity, and reusability toward the hydrogenation of nitrobenzene to p-aminophenol, with hydrogen as the reducing agent in sulfuric acid. The effects of P species on the catalyst structure, surface properties, and catalytic performance were investigated. It was found that the Pt/P-ACC catalyst had an excellent catalytic activity due to its smaller Pt nanoparticles and higher content of surface-active metal compared with Pt/ACC. Besides, the experimental results and in situ infrared studies demonstrated that the interaction effect between the Pt and P species imbued the surface of Pt with an electron-rich feature, which decreased the adsorption of electron-rich substrates (that is, phenylhydroxylamine) and prevented their full hydrogenation, leading to enhanced selectivity during the hydrogenation of nitrobenzene to p-aminophenol.

Phytate Coordination-Enhanced Electrocatalytic Activity of Copper for Nitroarene Hydrogenation through Concerted Proton-Coupled Electron Transfer.

Coupling acid-electrolyte proton exchange membrane fuel cells for electricity generation and cathodic hydrogenation for valuable chemical production shows great potential in energy and chemical industry. The key for this promising approach is the identification of cathode electrocatalysts with acid resistance, high activity, and low fabrication cost for practical applications. Among various promising cathodic candidates for this integrative approach, the easily available and cheap Cu suffers from low acidic hydrogenation activity due to kinetically arduous proton adsorption/activation. Inspired by the kinetic advantages of the concerted proton-coupled electron transfer (CPET) over the sequential proton-electron transfer process, herein, we use phytate coordination on Cu surface to overcome the kinetic bottleneck for proton adsorption/activation through the CPET pathway in an acidic half-cell setup; this leads to 1 order of magnitude activity enhancement (36.94-fold) for nitrobenzene hydrogenation. Mechanistic analysis confirms that phytate, as proton acceptor, induces the CPET process and overcomes the above kinetic limitations by tuning the d-band center and concentrating protons on the Cu surface. Consequently, the CPET process facilitates the formation of active hydrogen intermediates for efficient cathodic hydrogenation. This work provides a promising approach to integrate electricity generation and chemical production.

Residence time characteristic of Taylor reacting flow in a microchannel reactor

Herein, an in-situ visual method was developed to determine the residence time characteristic of a typical gas-liquid Taylor reacting flow in a microchannel reactor. Nitrobenzene hydrogenation was chosen as a reference heterogeneous reaction. The obtained results demonstrated the feasibility of the proposed in-situ visual method in determining the real residence time. The real residence time variation along with the flow distance is inherently related to the local nitrobenzene and hydrogen reactants consumption and mass transfer performance. The increase in residence time was initially accelerated due to rapid hydrogen consumption at the upstream. Then, ascribed to the gradually exhausted nitrobenzene, the deteriorated mass transfer resulted in the residence time being proceeded almost linearly increase along the flow direction at the downstream. Besides, the effects of both initial nitrobenzene concentration and liquid flow rate were also explored. This work reveals the intrinsic interaction between the residence time characteristic and catalytic reaction.

Multi-objective optimization of aniline and hydrogen production in a directly coupled membrane reactor

A numerical study of aniline production by hydrogenation of nitrobenzene (NBH) and hydrogen production by steam methane reforming (SMR) in a directly coupled membrane reactor is developed. This membrane reactor was proposed aiming to decarbonize heating in SMR and to favor the recovery of all products. Aniline recovery is improved in this reactor as water, a byproduct in NBH, is consumed in SMR. The simulation is performed using a heterogeneous-one dimensional model (Dusty gas model) and results are compared against the homogeneous model. The operating conditions of the reactor were selected using a multi-objective optimization method, genetic algorithms. The aims of the optimization were: methane conversion maximization, minimum membrane area, minimum reactor size, hydrogen yield maximization, nitrobenzene conversion maximization and the maximization of hydrogen recovery. This process was able to achieve complete conversion of methane and nitrobenzene. The hydrogen yield achieved can be as high as the maximum (∼4). 35% of this hydrogen was used as a reactant for aniline production. 99% of the unreacted hydrogen was recovered and purified. As the steam flow was minimized, aniline was obtained with a molar composition (70%), 2.1 times higher than that obtained in a conventional process for aniline production (33%). CO 2 was obtained with a purity of 97%, hence, CO 2 carbon capture and storage techniques were also favored. In addition, the energy requirements of heating of feedstock, reaction and recovery system of this novel process was 2.7 times lower than that of conventional processes carried out independently. • Operating conditions were selected through a multi objective optimization. • Energy requirements were reduced 2.7 times. • The recovery of the final products (aniline, hydrogen, and CO2) was favored. • Complete conversion of reactants was achieved. • A hydrogen efficiency of 99% was achieved.

Effect of Cu Content on Structure of NiCu Alloy Catalyst and Catalytic Performance for Nitroarenes Hydrogenation

AbstractCarbon doped silica‐supported NiCu alloy nanoparticles (Ni1Cux/C@SiO2) with different Cu/Ni molar ratio (x=0.12, 0.24, 0.36) were fabricated via one‐step impregnation, following in situ carbonization reduction. Effects of Cu content on catalyst structure, surface properties and particle sizes were investigated by Brunauer‐Emmett‐Teller (BET), inductively coupled plasma (ICP), Raman, X‐ray diffraction (XRD), transmission electron microscopy (TEM) and X‐ray photoelectron spectroscopy (XPS). The surface Ni0 content increased with increasing Cu content, but showed a maximum at 0.24 of Cu/Ni molar ratio, because the smaller NiCu alloy nanoparticle formed and the segregation of antioxidative Cu atoms on the surface protected the metallic Ni from oxidation. The Ni1Cux/C@SiO2 were investigated for nitrobenzene hydrogenation with H2. The optimal Ni1Cu0.24/C@SiO2 catalyst with the highest Ni0 content showed markedly improved catalytic activity compared to monometallic Ni/C@SiO2. The Ni0 species were the active sites for the hydrogenation of nitrobenzene. The Ni1Cu0.24/C@SiO2 could transform various substituted nitroarenes to corresponding aromatic amines. Moreover, the Ni1Cu0.24/C@SiO2 could be recycled for 8 times without decrease in catalytic performance, exhibiting superior anti‐oxidation and anti‐leaching abilities.

Effect of Flow Direction on a Double‐Duty Microreactor for Coproduction of Aniline and Hydrogen

AbstractA new thermally coupled microreactor, which simultaneously produces hydrogen and aniline, is simulated. It is suggested that the nitrobenzene hydrogenation process, the heat source, occurs in the tube section, thereby providing the requisite energy for the reactor system. Conversely, the shell section contains the steam reforming of glycerol coolant for the exothermic reaction. The results are evaluated in the two flow directions, namely, cocurrent and countercurrent. The furnace and cooling system, vital for the conventional steam reforming and aniline production processes, are eliminated, respectively, having accurately implemented the sensitivity analysis. Optimization of the most effective parameters is performed via genetic algorithm.

Unprecedentedly high activity and selectivity for hydrogenation of nitroarenes with single atomic Co1-N3P1 sites

Transition metal single atom catalysts (SACs) with M1-Nx coordination configuration have shown outstanding activity and selectivity for hydrogenation of nitroarenes. Modulating the atomic coordination structure has emerged as a promising strategy to further improve the catalytic performance. Herein, we report an atomic Co1/NPC catalyst with unsymmetrical single Co1-N3P1 sites that displays unprecedentedly high activity and chemoselectivity for hydrogenation of functionalized nitroarenes. Compared to the most popular Co1-N4 coordination, the electron density of Co atom in Co1-N3P1 is increased, which is more favorable for H2 dissociation as verified by kinetic isotope effect and density functional theory calculation results. In nitrobenzene hydrogenation reaction, the as-synthesized Co1-N3P1 SAC exhibits a turnover frequency of 6560 h−1, which is 60-fold higher than that of Co1-N4 SAC and one order of magnitude higher than the state-of-the-art M1-Nx-C SACs in literatures. Furthermore, Co1-N3P1 SAC shows superior selectivity (>99%) toward many substituted nitroarenes with co-existence of other sensitive reducible groups. This work is an excellent example of relationship between catalytic performance and the coordination environment of SACs, and offers a potential practical catalyst for aromatic amine synthesis by hydrogenation of nitroarenes.

Simple, controllable and environmentally friendly synthesis of FeCoNiCuZn-based high-entropy alloy (HEA) catalysts, and their surface dynamics during nitrobenzene hydrogenation

High-entropy alloys (HEAs) have rapidly become one of the hottest research topics in several fields, including materials science, corrosion technology, and catalysis because of their multiple advantages and their potential applications. In this study, using a novel straightforward electroless deposition method, multi-elemental alloys (FeCoNiCuZn) supported on graphite were prepared with controlled metal loading (HEA/g-X; X = 40, 80, 100) without any high temperature post-treatments. These materials were characterized using scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction, and showed a composition ranging from 11 at.% to 31 at.% for each metallic element, a total metal loading varying from 1.3 to 5.2 at.% (5.9 to 21.5 wt.%), homogeneous distribution, and an amorphous structure. Electrochemical impedance spectroscopy, cyclic voltammetry, linear sweep voltammetry, and chronoamperometry were used to evaluate the surface dynamics and the effect of the solution pH during the electrochemical hydrogenation of nitrobenzene using the HEA/g-40 material. The nitrobenzene conversion (>9 mmolNB gcat-1 h−1) and aniline production (≈ 4 mmolAN gcat-1 h−1) rates in Na2SO4 solution (at −1.0 V vs. Ag/AgCl) demonstrated a strong dependence on the applied potential. After comparing the results in alkaline medium (KOH), a competitive adsorption of species (nitrobenzene and H2O) was observed, showing a synergistic effect that greatly improved the selectivity of the nitrobenzene hydrogenation to aniline, from 23% in Na2SO4 to an outstanding 94% in KOH at the same applied potential, surpassing the results of a platinum electrode (34% in KOH). These results provide insightful information regarding the nature of the active sites involved in each step of the reaction mechanism, and gives useful means to develop new, tailored multifunctional HEA electrocatalyst materials.

CFD modeling of multiphase flows with detailed microkinetic description of the surface reactivity

The analysis of catalytic processes and the development of innovative technologies require a deep comprehension of the complex interplay between the intrinsic functionality of the heterogeneous material and the surrounding environment in the reactor. This is particularly important for multiphase catalytic reactors where complex interactions among the phases distribution, the inter- and intra-phase transport and the catalytic material occur. In this work, a computational framework has been developed to couple the solution of the hydrodynamics of multiphase flow using Computational Fluid Dynamics (CFD) with the detailed description of the surface reactivity through first-principles microkinetic models. In particular, the methodology employs an algebraic Volume-Of-Fluid (VOF) approach for the advection of the phases and takes advantage of the Compressive-Continuous Species Transfer (CST) for the modeling of the species mass interfacial transfer. The heterogeneous chemistry is included as source terms to the mass and energy equations acting at the catalytic surface, while the solution of the mass balance equation employs an operator splitting approach. The numerical framework has been assessed with respect to simple geometries by direct comparison with analytical and fully coupled solutions followed by examples of application in the context of the nitrobenzene hydrogenation to aniline. The envisioned approach is the first step toward the first-principles-based multiscale analysis of multiphase catalytic processes paving the way toward the detailed understanding and development of innovative and intensified technologies.

Role of Pd in the Electrochemical Hydrogenation of Nitrobenzene Using CuPd Electrodes

AbstractInterest in the electrochemical reduction of organic compounds as an alternative to hydrogen electrosynthesis is driven, among other reasons, by the fact that the products obtained in this process may have more economic value than H2. Furthermore, the technique, coupled with renewable sources of electricity, may open the door for large volume green chemical synthesis. In the present article, the electrochemical reduction and hydrogenation of nitrobenzene to aniline at neutral pH is focused upon, using copper electrodes with and without palladium decoration. Both electrodes present good activity, with a decrease in the overpotential for nitrobenzene reduction and the competing hydrogen evolution reaction when Pd is deposited in the surface of the Cu electrode. It is observed that the rate and selectivity of nitrobenzene reduction to aniline improves at high concentrations, obtaining yields close to 70% for 30 × 10−3 m initial concentrations of nitrobenzene when using Pd decorated Cu electrodes. Impedance spectroscopy analysis reveals that the role of Pd in the decorated electrodes is to enhance the production of H* radicals, necessary for the nitrobenzene reduction process. This explains the increase in the selectivity toward aniline production by the incorporation of small amounts of Pd in the surface of the Cu electrode.

Simultaneous synthesis of aniline and γ-butyrolactone from nitrobenzene and 1,4-butanediol over Cu-CoOx-MgO catalyst via catalytic hydrogen transfer process: Effect of calcination temperature

This study examined a hydrogen transfer reaction from 1,4-butanediol to nitrobenzene for γ-butyrolactone and aniline simultaneously over Cu-CoOx-MgO catalysts. The catalyst was developed by co-precipitation followed by metal hydroxycarbonate mixing and calcination at three different temperatures (500, 700, and 900 °C). The hydrogenation of nitrobenzene to aniline and the dehydrogenation of 1,4-butanediol to γ-butyrolactone was accomplished in a gas-phase fixed-bed continuous reactor system at 250 °C. The catalyst Cu-CoOx-MgO-500 calcined at 500 °C showed outstanding performance because of the higher copper dispersion and negligible spinel species (CuCo2O4 /MgCo2O4) compared to the other two catalysts. The order of activity decreased with increasing calcination temperature from 500° to 900°C. The activity trend followed the order, Cu-CoOx-MgO-500 > Cu-CoOx-MgO-700 > Cu-CoOx-MgO-900. The effect of calcination on the catalytic properties was analyzed by atomic absorption spectroscopy elemental analysis, Brunauer-Emmett-Teller surface area, N2O pulse chemisorption, temperature-programmed reduction-H2, X-ray diffraction, and X-ray photoelectron spectroscopy. The results showed that Cu-CoO-MgO-500 exhibited more active copper sites (Cu0/Cu+1) and optimal metal-support interactions that decrease the reduction temperature of copper. On the other hand, Cu-Co and Mg-Co spinel (CuCo2O4/MgCo2O4) content, which adversely affects the catalyst activity, increased with increasing calcination temperature. In summary, simultaneous hydrogenation and dehydrogenation reactions via hydrogen transfer reactions have potential commercial applications.