Reduction 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.

Bimetallic Fe–Cu metal organic frameworks for room temperature catalysis

Bimetallic Fe–Cu MOF was effectively synthesized through a one‐pot solvothermal process and successfully characterized by TEM, XPS, SEM, XRD, BET, EDX, elemental mapping, and FT‐IR analysis. This bimetallic MOF was employed as a catalyst in the reduction of nitroarenes at room temperature and as well as in the reduction of dyes, for example, methyl orange (MO) and methylene blue (MB). Results pointed to Fe–Cu MOF exhibiting outstanding catalytic performance for both room temperature reactions. The catalytic activity of Fe–Cu MOF in comparison with Fe‐MOF and Cu‐MOF in the nitroarenes reduction indicated a superior activity compared with single‐metal MOFs. Activity of Fe–Cu MOF catalyst did not change after its recycling and reusing for seven consecutive cycles in nitrobenzene reduction.

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.

Au Nanoparticles Supported by Porous Aromatic Frameworks—Efficient and Recyclable Catalysts for Nitro Reduction

A strategy has been developed for the preparation of gold nanoparticles (Au NPs) supported by porous aromatic frameworks (Au@PAF-184, Au@PAF-185) with high Au NPs loading, good stability and excellent activity. This approach contains two steps: the first step is ion exchange between cationic porous aromatic frameworks with NaAuCl4, fixing AuCl4− by the electrostatic interaction between anions and cations; the second step is reduction with NaBH4. Au@PAF-184 and Au@PAF-185 were successfully prepared accordingly. In comparison with the previously prepared similar types of materials such as Au@PAF-93 (2.86 wt% Au loading) and Au@PAF-94 (4.69 wt% Au loading) prepared by coordination and reduction, etc., the loading of Au NPs of Au@PAF-184 (24.2 wt% Au loading) and Au@PAF-185 (34.9 wt% Au loading) has increased by about 8 times. When employed as catalysts for nitrobenzene reduction, both Au@PAF-184 and Au@PAF-185 exhibited high catalytic activity and excellent reusability.

Facet-dependent Fe(II) redox chemistry on iron oxide for organic pollutant transformation and mechanisms

Fe(II) redox chemistry is a pivotal process of biogeochemical Fe cycle and the transformation of organic pollutants in subsurface aquifers, while its interfacial reactivity on iron oxides with varying surface chemistries remains largely unexplored. In this study, the redox processes of Fe(II) on two hematite with highly exposed {001} and {110} facets and their impacts on the transformation of nitrobenzene were investigated. Results suggest that Fe(II) adsorption is the rate-limiting step of the redox chain reactions, controlling the reduction potential (EH). Nitrobenzene activates the facet electron transfer on hematite, leading to nitrobenzene reduction and Fe(II) oxidation. Moreover, {001} facet exhibits a higher reactivity and electron transport efficiency than {110} facet, which is attributed to a lower site density (0.809 #Fe/nm2) and a lower EH of hematite {001} facet than that of {110} facet. It is worth noting that the facet-dependent reduction activity is more intense at low pH or high Fe(II) activity. A slight dissolution of {110} facet was observed, indicating hematite {001} facet exhibits higher thermodynamic stability than {110} facet. This study confirms the facet-dependent reducing activity of surface bound Fe(II) on hematite, providing a new perspective for in-depth understanding of the interfacial reactions on hematite. The findings of this work broaden the biogeochemical process of Fe cycle in subsurface environments and its impact on the fate of organic pollutants in groundwater.

Enhanced reduction of nitrobenzene derivatives using reusable Ni nanoparticles supported on multi-layered poly(1,2-phenylenediamine)-coated layered double hydroxides

Recently, nanomaterials with layered double hydroxide (LDH) cores have been the subject of intense research regarding their promising applications in organic synthesis. In this study, nitrobenzene reduction is investigated by designing and synthesizing a novel LDH-based heterogeneous catalyst containing a nickel-1,2-phenylenediamine complex. The Cu–Zn–Al LDH was functionalized with copolymer bearing a glycidyl methacrylate (GMA) linkage that makes it suitable for grafting with 1,2-phenylenediamine. Overall, the synthesized LDH@MPS-GMA-PDA-Ni was found to be a highly efficient heterogeneous nanocatalyst that can catalyze nitroarene reduction with high yields under mild conditions.

Impact of hole scavengers on photocatalytic reduction of nitrobenzene using cadmium sulfide quantum dots

One key factor that affects the reaction yield and selectivity of nanoparticle-catalyzed photochemical reactions is the type of hole scavengers. In this work, we examine the effect of hole scavengers in photoreduction of nitrobenzene catalyzed by cadmium sulfide quantum dots. We discover that the hole scavengers can determine the reduction pathway as well as the final product. Specifically, when methanol is the solvent and the sole hole scavenger, or when it is used in conjunction with ascorbic acid, ammonium formate, mercaptopropionic acid, or sodium borohydride, the reaction follows a direct reduction pathway. In contrast, with methanol and sodium sulfite, the reaction proceeds via a coupling route. Some hole scavengers directly participate in the redox reaction of intermediates. This study demonstrates that the type of hole scavenger can alter the reaction pathways and determine the reaction outcome and should be chosen with careful consideration. • Nitrobenzene is photo-catalytically reduced by CdS quantum dots with hole scavengers • Different hole scavenger combinations lead to different products • The type of hole scavenger affects reaction times and pathways The role of hole scavengers in photocatalysis is often regarded to be removing the holes in photocatalysts by donating electrons to them. Mureithi et al. show that the effect of hole scavengers goes beyond removal of holes to affecting the reaction time, pathways, and products in photocatalytic reactions.

Elementary mechanism for the electrocatalytic reduction of nitrobenzene on late-transition-metal surfaces from density functional theory

Reduction of nitrobenzene to aniline is important in the production of industrial chemicals and treatment of wastewater. The electrocatalytic mechanism of nitrobenzene reduction across late-transition-metal electrocatalysts is not well established, making rational electrocatalyst design challenging. Density functional theory (DFT) methods are used to identify elementary steps for nitrobenzene reduction and determine trade-offs that dictate optimizing electrocatalysts. Overall reduction activity is optimized based on a trade-off between activity for the initial reduction of the NO 2 -phenyl∗ and the reduction of surface-bound hydroxide (OH∗) species. The binding of O serves as a descriptor to predict the energetics of both steps, and the optimal electrocatalyst will have an intermediate O∗ binding strength. DFT results predict that, of close-packed late-transition-metal surfaces, the Cu (111), Ir (111), Pd (111), and Pt (111) metal surfaces will most effectively balance these trade-offs. Bimetallics that could offer high electrocatalytic activity for nitroaromatic reduction are suggested. • The first elementary reduction of R-NO 2 limits the rate of nitrobenzene reduction • Strong O binding poisons catalysts otherwise active for nitrobenzene reduction • Intermediate O binding leads to an optimal nitrobenzene reduction electrocatalyst The reduction of nitroaromatics is important in both the production of fine chemicals and the treatment of wastewater. Electrocatalytic reduction could offer an energy-efficient and scalable approach for these applications. The development of active and selective electrocatalysts is facilitated by elementary mechanism determination. We applied density functional theory to determine the rate-limiting steps in electrocatalytic nitrobenzene reduction over late-transition metals. A “volcano” trade-off dictated by the metals’ affinity for binding O was developed and used to predict single-metal and bimetallic surfaces that would optimize nitrobenzene electroreduction activity. Rate-limiting steps in electrochemical nitrobenzene reduction on late-transition-metal surfaces are determined using density functional theory calculations. A rationale for electrocatalyst optimization is presented and used to suggest optimal nitroaromatic reduction electrocatalysts.

Synergistic effect of bioanode and biocathode on nitrobenzene removal: Microbial community structure and functions

This study aimed to reveal the synergistic effect of bioanode and biocathode on nitrobenzene (NB) removal with different microbial community structures and functions. Single-chamber bioelectrochemical reactors were constructed and operated with different initial concentrations of NB and glucose as the substrate. With the synergistic effect of biocathode and bioanode, NB was completely removed within 8 h at a kinetic rate constant of 0.8256 h−1, and high conversion rate from NB to AN (92%) was achieved within 18 h. The kinetic rate constant of NB removal was linearly correlated with the maximum current density and total coulombs (R2 > 0.95). Increase of glucose and NB concentrations had significantly positive and negative effects, respectively, on the NB removal kinetics (R2 > 0.97 and R2 > 0.93, respectively). Geobacter sp. and Enterococcus sp. dominated in the bioanode and biocathode, respectively. The presence of Klebsiella pneumoniae in the bioanode was beneficial for Geobacter species to produce electricity and to alleviate the NB inhibition. As one of the dominant species at the biocathode, Methanobacterium formicicum has the ability of nitroaromatics degradation according to KEGG analysis, which played a crucial role for NB reduction. Fermentative bacteria converted glucose into volatile fatty acids or H2, to provide energy sources to other species (e.g., Geobacter sulfurreducens and Methanobacterium formicicum). The information from this study is useful to optimize the bioelectrocatalytic system for nitroaromatic compound removal.

Photocatalytic Multielectron Reduction of Nitroarenes to Anilines by Utilizing an Electron-Storable Polyoxometalate-Based Metal-Organic Framework.

A powerful approach to generate photocatalysts for the highly selective reduction of nitrobenzene using light as the driving force is a combination of photosensitizers and electron-storable components in a cooperative photocatalysis fashion. Herein, a new precious metal-free photocatalyst, {ZnW-TPT}, was prepared by incorporating a Zn-substituted monovacant Keggin polyanion [SiZnW11O39]6- and a photoactive organic bridging link 2,4,6-tri(4-pyridyl)-1,3,5-triazine (TPT) into a framework. In this structure, the direct coordination bond between [SiZnW11O39]6- and the TPT ligand and the π-π interactions between TPT molecules help separate and migrate photogenerated carriers, which improves the photocatalytic activity of {ZnW-TPT}. The photoelectrochemical properties of {ZnW-TPT} were well studied by solid UV-vis absorption, fluorescence, transient photocurrent response, and electrochemical impedance spectroscopy tests. {ZnW-TPT} efficiently converts using hydrazine hydrate with 99% conversion and 99% selectivity for anilines under mild conditions.

A suitable modified high-rate cobalt immobilized on acid supported ionic liquid catalysed transfer hydrogenation of nitroarenes

The present study focuses on the selective reduction of various nitrobenzene to aniline using non-noble metals such as CoCl2 supported [Cemim]Br and formic acid as a hydrogen donor. Under ionic liquid medium, the CoCl2 is found to be very efficient in the selective reduction of nitroaromatics to aniline. The catalyst is reusable, and it can be used for six cycles without affecting the efficiency of the conversion.

Cu2O nanoparticles modified BiO2-x nanosheets for efficient electrochemical reduction of nitrate-N and nitrobenzene from wastewater

Nitrogen-polluted wastewater posed great threat to the environment and human beings. Bismuth-based materials have presented high potentials for wastewater treatment. However, it suffers from unsatisfactory electrocatalytic efficiency, especially for nitrate-N removal. Considering the superior performance of copper in electrochemical reduction reactions, Cu2O nanoparticles modified BiO2-x nanosheets (Cu2O NPs/BiO2-x NSs) were designed and synthesized through a one-step hydrothermal method for wastewater purification. The obtained Cu2O NPs/BiO2-x NSs presents enhanced electrocatalytic activity towards nitrate removing, since the introduced Cu2O NPs not only increased the active sites but also decreased the electrical resistance. The effect of reaction parameters (current density, initial concentration, initial pH, supporting electrolyte, and dissolved oxygen) was also studied to optimize the operation conditions. Meanwhile, the electrochemical and scavenging experiments illustrated the mechanism that both the direct electron transfer and atomic H* played important roles in nitrate reduction. Furthermore, when applying Cu2O NPs/BiO2-x NSs for the treatment of nitrobenzene (NB), it achieved nearly 90% removal efficiency of NB in 30 min. Therefore, the designed Cu2O NPs/BiO2-x NSs shows a wide range of potential for removing both nitroaromatic and inorganic nitrogen pollutants.

Enhanced nitrobenzene removal in soil by biochar supported sulfidated nano zerovalent iron: Solubilization effect and mechanism

Sulfidated nano zerovalent iron (S-nZVI) is reported to be effective in removal of aqueous organic contaminants. However, little is known about its potential use in reductive degradation of soil-sorbed contaminants. In this study, biochar (BC) supported S-nZVI (S-nZVI@BC) was successfully synthesized through sulfidation and carbon loading modification, which effectively combined the solubilization characteristics of BC and high reduction characteristics of S-nZVI. Transmission electron microscopy (TEM) with an energy-dispersive X-ray spectroscopy (EDS) analysis suggested that sulfur and iron were evenly distributed throughout BC matrix. The degradation of nitrobenzene (NB) in soil was achieved more efficiently with the as-synthesized S-nZVI@BC composites. Results indicated that S-nZVI@BC with S-nZVI/BC mass ratio of 3:1, dosage of 10 mg/g exhibited superior NB removal (98%) and aniline (AN) formation (90%) efficiency within 24 h without formation of other intermediates, higher than those of S-nZVI. Meanwhile, the surface FeSX layer enhanced the antioxidant capacity of S-nZVI@BC and participated in the reduction of NB. The soil-sorbed NB decreased from 14% to 1.4%, indicating that the addition of BC played an important role in solubilization of NB from soil. Solubilization-reduction was the dominant mechanism for NB removal. This research indicated that S-nZVI@BC held the potential to enhance in-situ remediation of NB-contaminated soil.

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.

Sol-gel assembled MnCo2O4/rGO photocatalyst for enhanced production of aniline from photoreduction of nitrobenzene under visible light

Aniline is one of the most important chemicals for being a major compound in many industries such as plastics, explosives, dyes and other industries. Photocatalysis has displayed impressive results for the green production of aniline. In this investigation, simple sol-gel regime was adopted successfully to synthesize MnCo2O4 nanoparticles (NPs) that were subsequently dispersed on reduced graphene oxide (rGO) in the progression of MnCo2O4/rGO nanocomposite. The results of the various analyzes revealed that prepared nanocomposites possessed improved absorption in the visible light region implying that photocatalytic effectiveness of these materials will increase significantly in this region of radiation. Inclusion of 15 wt% of rGO to MnCo2O4 NPs contributed remarkably to the bandgap regression from 1.90 to 1.66 eV. The results derived from photoluminescence and transient photocurrent experiments verified that photoinduced charges within the prepared MnCo2O4/rGO nanocomposites have weak capability to recombine. It has been shown that nitrobenzene could be reduced entirely into aniline over the optimized MnCo2O4/rGO nanocomposite when subjected to visible light for 30 min. Recycled photocatalysts displayed considerable durability and stability when reused many durations for nitrobenzene reduction. Synthesized nanocomposites could be applied on a larger scale to prepare many organic compounds under the visible light illumination.

Phase Evolution, Polymorphism, and Catalytic Activity of Nickel Dichalcogenide Nanocrystals

The nickel chalcogenide family contains multiple phases, each with varying properties that can be applied to an expansive range of industrially relevant processes. Specifically, pyrite-type NiS2 and NiSe2 have been used as electrocatalysts for oxygen or hydrogen evolution reactions. These pyrites have also been used in batteries and solar cells due to their optoelectronic and transport properties. The phase evolution of pyrite NiS2 and polymorphism of NiSe2 have briefly been studied in the literature, but there has been limited work focusing on the phase transformations within each of these two systems. Using experiments and calculations, we detail how pyrite NiS2 nanocrystals decompose into hexagonal α-NiS, and how the synthesis of pyrite NiSe2 nanocrystals is affected by the presence of two polymorphs, a metastable orthorhombic marcasite phase and a more stable cubic pyrite phase. Each reaction can be controlled by fine-tuning the reaction parameters, including temperature, time, and the precursor identity and concentration. Interestingly, both NiS2 and NiSe2 nanopyrites are active catalysts in the selective reduction of nitrobenzene to aniline, in agreement with other catalysts containing an fcc (sub) lattice. Our results demonstrate a feasible, logical process for synthesizing nanocrystalline pyrites without common byproducts or impurities. This work can help in solving a major problem suspected in preventing pyrite FeS2 and similar materials from large-scale use: the presence of small amounts of secondary phases and impurities.

Performance of graphitic carbon nitride nanosheets derived from liquid and thermal exfoliations towards the electrochemical reduction of nitrobenzene

The electrocatalytic activity of graphitic carbon nitride nanosheets prepared via thermal and solvent exfoliation is compared towards nitrobenzene reduction.

An intriguing tetranuclear Rh-based polyoxometalate for the reduction of nitroarene and oxidation of aniline.

An organic-inorganic hybrid polyoxometalate Na5H5.68 [Na0.17Rh0.83III(C6H8N2)2Cl2]2(C8H8N2)2[As4W40O140Rh4IV(C6H4N2S)2]·nH2O (1) containing 5.66 Rh atoms is prepared; to our knowledge, it owns the largest number of Rh atoms in the Rh-POM family. Compound 1 demonstrates good catalytic performance in the reduction of nitrobenzene to aniline and the oxidation of aniline to azobenzene under mild conditions. Moreover, catalyst 1 exhibits high activity, excellent stability and recyclability.

Metal–free C2N doped with sp2–hybridized B atom as high–efficiency photocatalyst for nitrobenzene reduction reaction: A density functional theory study

Developing low–cost and efficient materials for nitrobenzene reduction reaction (NBRR) is attractive and challengeable. Great research efforts have been made in metal–based materials, while the metal–free catalysts for nitrobenzene (Ph–NO2) conversion have been rarely explored. Herein, by means of density functional theory (DFT) calculations, the potential of B–doped C2N as metal–free photocatalyst for NBRR was systematically investigated. The results reveal that the sp2–hybridized B doped C2N at N site (BN–C2N) exhibits high catalytic activity for nitrobenzene conversion to aniline (Ph–NH2) with a low limiting potential of –0.30 V. Besides, BN–C2N can improve the photoconversion efficiency by broadening the light absorption of C2N. Therefore, BN–C2N is a promising metal–free photocatalyst for NBRR, which may open a new avenue for Ph–NO2 conversion under ambient conditions.