Conversion Of Nitrobenzene Research Articles

Single Pt atom decorated graphitic carbon nitride as an efficient photocatalyst for the hydrogenation of nitrobenzene into aniline

The hydrogenation of nitrobenzene into aniline is one of industrially important reactions, but still remains great challenge due to the lack of highly active, chemo-selective and eco-friendly catalyst. By using extensive density functional theory (DFT) calculations, herein we predict that single Pt atom decorated g-C3N4 (Pt@g-C3N4) exhibits excellent catalytic activity and selectivity for the conversion of nitrobenzene into aniline under visible light. The overall activation energy barrier for the hydrogenation of nitrobenzene on single atom Pt@g-C3N4 catalyst is even lower than that of the bare Pt(111) surface. The dissociation of N–O bonds on single Pt atom is triggered by single hydrogen atom rather than double hydrogen atoms on the Pt(111) surface. Moreover, the Pt@g-C3N4 catalyst exhibits outstanding chemoselectivity towards the common reducible substituents, such as phenyl,–C=C,–C≡C and–CHO groups during the hydrogenation. In addition, the doped single Pt atom can significantly enhance the photoconversion efficiency by broadening the light absorption of the pristine g-C3N4 to visible light region. Our results highlight an interesting and experimentally synthesized single-atom photocatalyst (Pt@g-C3N4) for efficient hydrogenation of nitrobenzene to aniline under a sustainable and green approach.[Figure not available: see fulltext.].

PVA‐encapsulated Palladium Nanoparticles: Eco‐friendly and Highly Selective Catalyst for Hydrogenation of Nitrobenzene in Aqueous Medium

In aqueous medium without any other additives, palladium (Pd) nanoparticles with water-soluble polyvinyl alcohol (PVA) as stabilizer were synthesized for the catalytic hydrogenation of nitrobenzene. Under the optimum experimental conditions, the nitrobenzene conversion and the selectivity for aniline were 99.3 % and 100 %, respectively. Comprehensive characterization methods, including TEM, UV/Vis, confocal laser scanning microscopy (CLSM), XRD and XPS allowed a better understanding of the role of PVA aggregates and the properties of Pd nanoparticles. The nitrobenzene conversion exceeded 80 % even after 6 cycles without any treatment of the catalyst. A mechanism about the hydrogenation of nitrobenzene catalyzed by Pd/PVA system was proposed. The Pd/PVA catalyst also exhibited excellent activity and selectivity, particularly to ortho-fluoronitrobenzene and ortho-nitrotoluene. This research can provide a reference for the environmentally friendly catalysis for hydrogenation of nitrobenzene and other substituted nitrobenzene compounds.

One-pot solvothermal synthesized CoS2@MoS2 nanocomposites for selective reduction coupling reaction to synthesize imines

Selective reduction coupling of nitroaromatics and aldehydes for imines synthesis has been investigated by using a series of bifunctional CoS2@MoS2 catalysts prepared by one-pot solvothermal method. Under optimal Co/Mo ratio of 0.75 and preparation temperature (180 °C), CoS2@MoS2–180-0.75 catalyst shows 96.5% nitrobenzene conversion, 93.0% imine selectivity and good versatility for substituted nitrobenzene and different aldehydes under mild conditions (60 °C, 1.5 MPa H2). The characterizations reveal that high nitroaromatics hydrogenation activity and good selectivity are mainly due to the formation of CoMoS phase, the coupling reaction between aniline derivatives and aldehydes is achieved by the appropriate acidity of CoS2@MoS2 nanocomposites.

Room temperature catalytic reduction of nitrobenzene to azoxybenzene over one pot synthesised reduced graphene oxide decorated with Ag/ZnO nanocomposite

We report herein, a one-pot synthetic route for the synthesis of reduced graphene oxide decorated Ag/ZnO nanocomposite and studied its catalytic activity as simple, recyclable and efficient catalyst for one-pot conversion of nitrobenzene to azoxybenzene. It was observed that 5–10 nm Ag-nanoparticles supported on 40–60 nm ZnO nanorod decorated on reduced graphene oxide was formed with a silver loading of 1.6 wt%. The effect of different reaction parameters were investigated and studied in detail. A nitrobenzene conversion of 96% with 98% selectivity of azoxybenzene was achieved without the use of any external additives.

Gas consumption characteristics determined by gas-liquid two-phase flow coupled with catalytic reaction in a gas-liquid-solid microreactor

In this work, the gas consumption characteristics were investigated by gas-liquid two-phase flow in a capillary microreactor using the catalytic hydrogenation of nitrobenzene as a reference gas-liquid reaction. Image processing technique was used to measure the gas consumption from the variation in the gas phase through the recorded images. The influence of the inlet nitrobenzene concentration and both the gas and liquid flow rates on the gas consumption and the microreactor performance was investigated. The experimental results showed that there existed a discrete hydrogen consumption process, i.e. the waiting stage and inburst stage. Hydrogen consumption was mainly attributed to the waiting stage in each bubble formation cycle. Minimal hydrogen was consumed in the inburst stage. In addition, there was a clear difference between the H2 consumption rates under each operating condition. As the gas flow rate and nitrobenzene concentration increased, the H2 consumption rate was gradually decreased with each successive formation cycle. Although the consumption rate was gradually reduced with each successive formation cycle with increasing liquid flow rate, the downward trend became increasingly gradual and clearly stabilized at 20 μL/min. The microreactor performances under different operating conditions were also investigated. The results showed that the nitrobenzene conversion was first increased and then gradually decreased with increasing the gas flow rate, whereas it was gradually decreased with increasing both the liquid flow rate and nitrobenzene concentration. The results obtained in this work are beneficial for not only understanding process intensification but also promoting the use of microreactor technology in additional industrial applications.

A Versatile, Mild and Selective Reduction of Nitroarenes to Aminoarenes Catalyzed by CeO2 Nanoparticles with Hydrazine Hydrate

AbstractA simple and convenient protocol is reported for the conversion of nitroarenes to aminoarenes by employing CeO2 nanoparticles (n‐CeO2) as heterogeneous solid catalysts using hydrazine hydrate as reducing agent under mild reaction conditions. A quantitative conversion of nitrobenzene is achieved using n‐CeO2 as solid catalyst with aniline selectivity to 93%. Further, this catalyst is also effectively used to transform wide range of nitroarenes to their respective aniline derivatives in higher conversions and selectivities. The reaction is found to be heterogeneous by leaching experiment and n‐CeO2 can be used for three cycles with no drop in its activity. Furthermore, the analyses of the fresh and three times used n‐CeO2 samples by powder X‐ray diffraction (XRD), UV‐Vis diffuse reflectance spectra (DRS), Fourier Transform‐Infrared Spectroscopy (FT‐IR), scanning electron microscope (SEM) and transmission electron microscope (TEM) indicate that the structural integrity, surface morphology and particle size remain unaltered during the course of the reaction. Furthermore, the valence state of Ce in n‐CeO2 is identical in the fresh and three times used samples as evidenced by Fourier Transform Raman spectroscopy. Some of the salient features of this process are operational simplicity, high conversion/selectivity, functional group tolerance, absence of noble metals/additives and reusability of the catalyst.

Synergism of Pt nanoparticles and iron oxide support for chemoselective hydrogenation of nitroarenes under mild conditions

An efficient and low-cost supported Pt catalyst for hydrogenation of niroarenes was prepared with colloid Pt precursors and α-Fe2O3 as a support. The catalyst with Pt content as low as 0.2 wt% exhibits high activities, chemoselectivities and stability in the hydrogenation of nitrobenzene and a variety of niroarenes. The conversion of nitrobenzene can reach 3170 molconv h−1 molPt−1 under mild conditions (30 °C, 5 bar), which is much higher than that of commercial Pt/C catalyst and many reported catalysts under similar reaction conditions. The spatial separation of the active sites for H2 dissociation and hydrogenation should be responsible for the high chemoselectivity, which decreases the contact possibility between the reducible groups of nitroarenes and Pt nanoparticles. The unique surface properties of α-Fe2O3 play an important role in the reaction process. It provides active sites for hydrogen spillover and reactant adsorption, and ultimately completes the hydrogenation of the nitro group on the catalyst surface.

Chemoselective hydrogenation of nitrobenzenes activated with tuned Au/h-BN

The azo- and hydrazo compounds are of great importance in pharmaceuticals, agrochemicals, and chemistry. The controlled reduction of nitroarenes to their coupled products such as aromatic azo and hydrazo compounds has been an interesting area of research synthetically and mechanistically. Herein, we report that the chemoselective catalytic hydrogenation of nitrobenzenes to hydrazobenzenes via azobenzenes can be achieved over gold nanoparticles supported by hexagonal boron nitride nanoplates. It is found that the catalytic process can be successfully conducted not only in N2 but also in air with isopropanol alcohol/KOH. Complete conversion of nitrobenzenes and high selectivity of azobenzenes and hydrazobenzenes have been achieved in one pot under N2 or air atmosphere. Furthermore, as usual unstable intermediates in the reduction process of nitrobenzenes, azobenzenes and hydrazobenzenes can be alternatively harvested as the main product by controlling reaction time or atmosphere. This work shows promise for direct and chemoselective synthesis of azo- and hydrazo compounds under mild conditions in a controllable manner.

Preparation of Pt[sbnd]Pd supported catalysts and investigation of its performance in one stage hydrogenation of nitrobenzene

Para aminophenol is one of the most important intermediates in chemical industries and pharmaceuticals. The present study describes the preparation of para aminophenol with single-step catalytic hydrogenation of nitrobenzene in acidic medium using platinum, palladium and bimetallic supported carbon active catalysts. Synthesized catalysts were characterized using X-ray diffraction, Scanning electron microscopy, temperature-programmed desorption of adsorbed NH3, and inductively coupled plasma. At 4.65% loading of platinum on carbon, the nitrobenzene conversion and selectivity to para aminophenol were favored under 80 °C and 1 bar H2 pressure. The quantitative analysis of samples was carried out using gas chromatography method followed by Mass and NMR spectroscopy in order to characterize the intermediates and products.

Studying the Three-Phase Hydrogenation of Nitrobenzene to Aniline in the Presense of a Ruthenium Catalyst

The results are presented from studying the catalytic properties of ruthenium catalyst 3% Ru/MN270 based on hypercrosslinked polystyrene in the reaction of three-phase hydrogenation of nitrobenzene to aniline. The following parameters are varied in the study: the NB concentration in the range from 0.12 to 0.24 mol/L, the catalyst concentration in the range from 1.11 × 10−4 to 11.12 × 10−4 mol/L, the temperature in the range from 160 to 190°C, and the partial hydrogen pressure in the range from 1.013 to 0.113 MPa. The optimum parameters of the process are determined, allowing 97% conversion of nitrobenzene and a selectivity of 98% towards aniline to be achieved.

One-step synthesis of Ru/montmorillonite composite from gel system of RuCl3-Na2O-ZnO-Al2O3-SiO2-F-H2O and applications in nitrobenzene hydrogenation catalysis

One-step synthesis of Ru/montmorillonite (Ru/Mt) without using any organic ligands has been successfully implemented from a gel system of RuCl3-Na2O-ZnO-Al2O3-SiO2-F−–H2O, and the catalytic application was demonstrated in the hydrogenation of nitrobenzene (NB). The synthesized materials were characterized by X-ray diffraction, infrared spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. Due to the particular structure of which Ru(0)-nanoparticles were encapsulated by clay layers, the catalytic activity of Ru/Mt. was found to experience no significant deactivation after runs of reactions. The catalytic performance of Ru/Mt. was determined as a function of Ru loading amount with respect to NB. The conversion of NB to aniline was found to reach 99.42% within 2.0 h (PH2 = 5.0 Pa; T = 90 °C), and the turnover frequency was higher than activated carbon- or Al2O3-supported- ruthenium catalysts (Ru/AC, Ru/Al2O3). The method has its priority in getting pure clay supports, and high catalytic activity was obtained by avoiding the paramagnetic ions from natural clays.

SiO2-coated zero-valent iron nanocomposites for aqueous nitrobenzene reduction in groundwater: Performance, reduction mechanism and the effects of hydrogeochemical constituents

Nanoscale zero-valent iron (nZVI) surface modification provides an effective way for in-situ remediation of nitrobenzene (NB) contaminated groundwater. However, it may bring some problems such as secondary pollution and ecotoxicity; moreover, the activity of modified nZVI was also vulnerable to the hydrogeochemical constituents of groundwater (e.g. pH, common ions). SiO2-coating technology is a promising approach to reduce secondary pollution, enhance the biocompatibility and improve the insensitivity of nZVI to the changes of the surrounding environment during contamination degradation process. In this study, the SiO2-coated nZVI composites were prepared and characterized; the microscopic mechanism and performance of NB reduction by SiO2-coated nZVI composites were studied; the effects of hydrogeochemical constituents of groundwater (e.g. pH, common ions) on NB reduction were investigated. The results indicated that SiO2-coating technology provided permeable mesh structure, which could facilitate aqueous NB to contact and react with the internal nZVI; in the reaction process, nitrosobenzene and azoxybenzene were detected as the intermediate and the maximum degradation capacity for thoroughly converting aqueous NB to aniline (AN) was approximately 366.3 mg/g, which was 3.75 times higher than that of bare nZVI. Furthermore, the synthesized composite showed no significantly reactivity restriction in the alkaline (pH, 5∼7) groundwater environment; Na+, K+, Cl−, NO3- and SO42- had no effect on the activity of the synthesized composite; Ca2+ and Mg2+ exhibited an inhibitory effect and HCO3- had an enhancement effect on the conversion of NB to AN. Overall, this study demonstrated the superiority of SiO2-coated nZVI composites and provided useful information for the future application in groundwater remediation.

Photoelectrocatalytic reduction of nitrobenzene on Bi-doped CuGaS2 films

Nitrobenzene, a toxic nitroaromatic, a feedstock compound to the production of many commercially relevant chemicals were photoelectrocatalytically reduced into aniline on a photoelectrode comprised by a bismuth-doped CuGaS2 nanocrystallyne thin films on molybdenum. The activity of the photoelectrodes were compared to the reaction performed on undoped-CuGaS2 films, and they were carried out under illumination with an applied bias potential at 0.9 V. Aniline was highly selectively obtained with 83% of conversion for reaction times of 100 min when using Bi-doped CuGaS2, representing higher conversion of nitrobenzene and yield to aniline than the undoped photoelectrode. The catalytic performance of the doped films remained stable for a set of 5 consecutive experiments. These results indicate Bi-doped CuGaS2 as a promising material to be applied in the photoelectrocatalytic reduction of nitrobenzene into aniline through the direct pathway mechanism, using solar light illumination.

Counting surface redox sites in carbon-supported electrocatalysts by cathodic stripping of O deposited from N2O

Methods of determining in situ the electrochemically active surface area of bulk noble metal electrodes (e.g., underpotential deposition of a strongly interacting sorbent followed by columbic stripping) may not be appropriate for certain base metals supported on electroactive supports, such as carbon, because of the difficulty of finding a metal-specific titrant and because the support itself can contribute a very large background current. For example, the coulometric stripping of metal-selective sorbates, like carbon monoxide, works for the in situ characterization of certain electrode-supported metals (e.g. Pt, Pd) if applied carefully, but not for base metals, like Cu that do not strongly adsorb the titrant. Moreover, in scoping studies, we found that underpotential deposition of Tl on carbon-supported Cu failed to be selective for the copper. Here we present the use of gentle oxidation of the metal domains using N2O as the oxidant, followed by cathodic stripping of the surface oxide. The method compares approximately with XRD line broadening for characterizing ∼10 nm particles of Cu supported on graphite felt. More significantly, we show that the method usefully normalizes the rates of two electrochemical hydrogenation reactions: conversion of nitrobenzene to aniline and conversion of benzaldehyde to benzyl alcohol.

Tube-in-tube hollow fiber catalytic membrane microreactor for the hydrogenation of nitrobenzene

The miniaturization of membrane reactors aims to improve the mass transfer efficiency. A tube-in-tube hollow fiber catalytic membrane microreactor that contains dual characteristics of a catalytic membrane reactor and a microreactor was developed in this study. For a gas-liquid-solid (G-L-S) reactor, the immobilization of solid catalysts on a hollow fiber membrane (HFM) via layer-by-layer (LBL) self-assembly enables the model reaction of nitrobenzene hydrogenation to occur. The unique structure of the novel catalytic membrane microreactor separates the gas and liquid reactants and shortens the transfer distance. The experimental results showed that the nitrobenzene conversion was high during 30 h of continuous operation. The effects of the flow rates and inlet nitrobenzene concentration were also investigated. At a given gas flow rate, the nitrobenzene conversion and concentration of the product aniline decreased with increasing the liquid flow rate. Meanwhile, at a given liquid flow rate, an increase in the gas flow rate led to an increase in the pressure of the gas phase. Sufficient hydrogen promoted the reaction, increasing the nitrobenzene conversion and aniline concentration. In addition, the inlet nitrobenzene concentration affected the conversion. Higher concentration not only enhanced the reaction rate but also caused catalyst poisoning. Based on these results, the newly designed catalytic membrane microreactor is feasible to improve the performance towards multiphase reaction.

Studies of Three-Phase Hydrogenation of Nitrobenzene to Aniline in the Presence of a Ruthenium Catalyst

Catalytic hydrogenation of nitrobenzene (NB) is an important technological stage in the production of aniline (AN). The catalytic behavior of hypercrosslinked polystyrene based ruthenium catalyst 3%Ru/MN270 in three-phase hydrogenation of NB to AN is discussed in the paper. The following parameters were varied during the studies: 0.12 to 0.24 mol/L NB, 1.11·10–4to 11.12·10–4mol/L catalyst, 160 to 190 °C, partial hydrogen pressure of 0.113 to 1.013 MPa. The optimal process parameters were determined to provide 98 % selectivity to aniline at 97 % conversion of nitrobenzene.

In Situ Generation of Cu0 Supported on TiO2 Aerogel as a Catalyst for the Vapour Phase Hydrogenation of Nitrobenzene to Aniline

This study is first to demonstrate a new strategy to synthesize Cu nanoparticles (NPs) supported on TiO2 (Cu@TiO2) catalyst towards the vapor phase hydrogenation of nitrobenzene. The experimental design involved the four different loadings (10, 15, 20 and 30 wt%) of Cu NPs onto the TiO2 aerogel to produce a complex with high surface area and increased pore volume. The developed catalysts were characterized using N2 physisorption analysis, powder-XRD studies, H2-temperature programmed reduction, field emission scanning electron microscopy–EDAX, high resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The characterisation results specified that the surface area, mesoporosity, the effective dispersion of Cu nanoparticles onto the TiO2 support exerted a significant influence on their catalytic activities. Further, it was found that the resulted process led to the complete in situ reduction of Cu2+ to Cu0, and fine dispersion of Cu0 NPs on the surface of TiO2. Thus, no further pre-reduction of the catalyst was required. The optimized 20 wt% Cu@TiO2 catalyst achieved about 94% nitrobenzene conversion with maximum aniline selectivity (> 98%), with enhanced stability where the catalyst was found to be active up to 15 h of continuous catalytic reactions. From the study, it is found that this approach is promising and provides insights into the fundamental understanding on the importance of aerogel materials as versatile catalysts.

Highly selective reduction of nitroarenes by sc-isopropanol in the presence of zirconia in a flow reactor

Reduction of nitroarenes using supercritical isopropanol as a source of hydrogen was studied in a flow reactor in the presence of zirconia at temperatures of 515 − 630 K and with residence time about 10 min. Zirconia was shown for the first time to be an effective and selective catalyst for transfer hydrogenation of nitroarenes. The use of complex supercritical fluid iPrOH/CO2 provided 100% selectivity for aniline at 95% conversion of nitrobenzene. In the absence of CO2, the selectivity was reduced due to formation of alkoxylation and N-alkylation by-products. The system can also be used for highly selective reduction of bromonitrobenzene avoiding undesired hydrodehalogenation.

One-pot synthesis of secondary amine via photoalkylation of nitroarenes with benzyl alcohol over Pd/monolayer H1.07Ti1.73O4·H2O nanosheets

The photoalkylation of nitroarenes with benzyl alcohols in one pot at room temperature and 1 atm N2 was achieved over the Pd/H1.07Ti1.73O4·H2O nanosheets. The sample shows efficient photocatalytic activity with high conversion of nitrobenzene (99%) and selectivity of secondary amine (85%). This flexible photocatalytic system is also applicable to other nitroarenes with high efficiency. Results of in situ FTIR, DRS, and in situ ESR revealed that the benzyl alcohol and nitrobenzene molecules can bind with the surface Lewis and Brønsted acid sites in the catalyst via the HO⋯Ti and NO2⋯HOTi species. The formation of surface coordination species results in not only the activation of reactant molecules via surface electron transfer, but also the expanded visible light absorption of the catalyst. Moreover, in situ ESR suggested that the surface coordination can also facilitate the formation of oxygen vacancies in catalysts, which can greatly promote the exposure of Lewis sites and enhance the activation of reactant molecules. Finally, a possible hydrogen transfer strategy over the sample is proposed on a molecular level.

Acid-treated bentonite-supported Ni catalysts via rapid microwave-assisted drying for nitrobenzene hydrogenation

ABSTRACTAcid-treated bentonite-supported Ni catalysts were prepared using a microwave-assisted drying process, characterized and used for the hydrogenation of nitrobenzene to aniline. Microwave-assisted drying of the catalyst reduced the drying time from 3 h with a traditional heating method to 10 min; after drying by microwave irradiation, the acid-treated bentonite-supported Ni catalysts were more stable due to a smaller crystallite size, a higher dispersion of metallic Ni and stronger interactions between Ni and the acid-treated bentonite support than the traditional drying method. Catalytic studies conducted at 300°C with a nitrobenzene liquid hourly space velocity of 3.6 mL g−1 h−1 and a H2 gas hourly space velocity of 4,800 mL g−1 h−1 indicated that the catalyst prepared using the microwave heating method maintained a nitrobenzene conversion of >99.9% with an aniline selectivity >93% during a 60-h reaction. In addition, the catalyst dried using a traditional method only functioned for 16 h.