Catalytic Hydrogenation Of Nitrobenzene Research Articles

Insights into the Mechanism of Nitrobenzene Reduction to Aniline by Phosphomolybdic Acid Supported TM1 Single-Atom Catalysts.

Catalytic hydrogenation of nitrobenzene (Ph-NO2) to aniline (Ph-NH2) is a model reaction in the field of catalysis, in which the development of efficient catalysts remains a great challenge due to the lack of strategies to solve activity and selectivity problems. In this work, the mechanism of Ph-NO2 hydrogenation over Pt1 supported on phosphomolybdic acid (α-PMA) was proposed by density functional theory (DFT) calculations. The results show that the dissociation of the first and second N-O bonds is triggered by single H-induced and double H-induced mechanisms, respectively. The limiting potential of the reaction process is -0.19 V, which is the smallest potential in the field of Ph-NO2 reduction reaction to date. In the whole reaction process, the catalytic active site is the Pt atom, and polyoxometalate plays the role of an electronic sponge in the reaction. Additionally, based on experimentally confirmed Pt1/Na3PMA, the reduction capacity of Pd1/Na3PMA toward Ph-NO2 was predicted by DFT calculation. The distinctive adsorption patterns of Ph-NO2 on Pt1/Na3PMA and Pd1/Na3PMA were elucidated using the DOS diagram and fragment molecular orbital analysis. We anticipate that our theoretical calculations can provide novel perspectives for experimental researchers.

Structure–Activity Relationship for the Catalytic Hydrogenation of Nitrobenzene by Single Platinum Atoms Supported on Nitrogen-Doped Carbon

Structure–Activity Relationship for the Catalytic Hydrogenation of Nitrobenzene by Single Platinum Atoms Supported on Nitrogen-Doped Carbon

Palladium decorated nickel and zinc ferrite spinel nanoparticles applied in aniline synthesis – development of magnetic catalysts

Aniline is one of the most important chemical in the polyurethane industry and it is produced by the catalytic hydrogenation of nitrobenzene. The development of novel, multifunctional catalysts, which are easily recoverable from the reaction mixture is therefore of paramount importance. Transition metal-containing ferrites decorated with palladium were prepared by using a combination of sonochemical and combustion steps. First of all, magnetic ferrites were produced to be used in catalyst preparation as supports for palladium nanoparticles. On the surface of the ferrite particles palladium nanoparticles were deposited by applying ultrahigh sonication in an alcoholic phase. All in all, three magnetic catalysts, Pd/NiFe2O4, Pd/ZnFe2O4, and Pd/NiZnFeO4 have been created. The catalysts have been tested and their activity have been compared in nitrobenzene hydrogenation to synthesize aniline at four different temperatures, and 20 bar pressure. The most active catalysts were the Pd/ZnFe2O4 and Pd/NiZnFeO4 systems with which aniline yields of 99.2 and 92.8 n/n% were achieved after 3 h of hydrogenation, respectively. In contrast, by applying the Pd/NiFe2O4 catalyst, a significantly lower aniline yield was achieved. It was proved that, due to their magnetic properties, the prepared catalysts are easily removable from the reaction medium by using a magnetic field. Thus, catalysts with excellent properties have been successfully developed and tested in nitrobenzene hydrogenation.

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.

Effect anions on the hydrogenation of nitrobenzene over N-rich Poly(ionic liquid) supported Pd catalyst

In this work, N-rich ionic liquid based on 1,3,5-triimidazole triazine was used to construct poly(ionic liquid) (PIL) through free radical polymerization, and support palladium nanoparticles (Pd NPs), which were used in the catalytic hydrogenation of nitrobenzene. The resulting N-rich PIL had a good dispersion effect and ultrafine Pd NPs as shown by SEM and TEM, thereby significantly enhancing the stability of the loaded metal NPs. The XPS results indicated that the metal-support interaction improved the catalytic performance of the catalyst. In particular, the effects of different anions (Tf2N-, PF6-, and Cl-) on the PILs were investigated, and the results showed that the Tf2N anion exhibited the best catalytic effect on the hydrogenation of nitrobenzene. Furthermore, density functional theory calculation confirmed that anions played a key role in activating the substrate in the hydrogenation of nitrobenzene. The corresponding results were consistent with the experimental results, which provided reference and research for the application of PILs in the future.

Three-Dimensional Network Pd-Ni/γ-Al2O3 Catalysts for Highly Active Catalytic Hydrogenation of Nitrobenzene to Aniline under Mild Conditions.

In view of the current situation of high cost and low catalytic efficiency of the commercial Pd-based catalysts, adding transition metals (Ni, Co, etc.) to form the Pd-M bimetallic catalyst not only reduces the consumption of Pd but also greatly improves the catalytic activity and stability, which has attracted increasing attention. In this work, the three-dimensional network Pd–Ni bimetallic catalysts were prepared successfully by a liquid-phase in situ reduction method with the hydroxylated γ-Al2O3 as the support. Through investigating the effects of the precursor salt amount, reducing agent concentration, stabilizer concentration, and reducing stirring time on the synthesis of the Pd–Ni nanocatalyst, the three-dimensional network Pd–Ni bimetallic nanostructures with four different atomic ratios were prepared under an optimal condition. The obtained wire-like Pd–Ni catalysts have a uniform diameter size of about 5 nm and length up to several microns. After closely combining with the hydroxylated γ-Al2O3, the supported Pd–Ni/γ-Al2O3 catalysts exhibit nearly 100% conversion rate and selectivity for the hydrogenation of nitrobenzene to aniline at low temperature and normal pressure. The stability testing of the supported Pd–Ni/γ-Al2O3 catalysts shows that the conversion rate still remained above 99% after 10 cycles. There is no doubt that the supported catalysts show significant catalytic efficiency and recyclability, which provides important theoretical basis and technical support for the preparation of low-cost, highly efficient catalysts for the hydrogenation of nitrobenzene to aniline.

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.

Ba-modified Ni-P amorphous alloy/acidified bentonite catalyst: preparation and the catalytic hydrogenation of nitrobenzene to aniline

In the present work, a Ba-modified Ni-P amorphous alloy/acid bentonite catalyst (Ni-P A/B) was prepared, and used for nitrobenzene hydrogenation to aniline in the liquid phase. The results showed that Ba addition could increase the dispersion of the active component Ni on the support and further form more Ni active centers. The addition of Ba could provide electrons for Ni, increasing the electron cloud density around Ni and improving the hydrogenation activity of the catalyst. At the condition of a Ba addition amount of 3.0%, a hydrogen pressure of 1.4 MPa, and a reaction temperature of 105 °C, the optimal nitrobenzene conversion and aniline selectivity was 99.0% and 98.9%, respectively. The catalyst maintained excellent stability when it was reused 10 times, which was 4 times greater than that of Ni-P A/B.

A step toward the numerical simulation of catalytic hydrogenation of nitrobenzene in Taylor flow at practical conditions

While computational studies on hydrodynamics of gas-liquid Taylor flow in microreactors are increasing, inclusion of mass transfer and reactions pose a challenge. Especially simulations for technically relevant reactions are lacking. This study undertakes a step in this direction by considering the hydrogenation of nitrobenzene to aniline. Physical properties are estimated from literature and a lack of data for practically relevant temperature and pressure is identified. By neglecting any feedback on hydrodynamics, the hydrogenation of nitrobenzene in a micro-channel is studied by two-dimensional numerical simulations with a volume-of-fluid method using a one-step reaction mechanism. Simulations are performed for three different bubble velocities at intermediate capillary numbers. Increase of bubble velocity enhances mass transfer and aniline production rate due to intensified recirculation in the liquid slug. Even for the channel height of 100 µm investigated here, the reaction is mass transfer limited and independent on initial concentration of hydrogen in liquid nitrobenzene.

Engineering nano-ordered of Ni nanoparticles on KIT-6 for enhanced catalytic hydrogenation of nitrobenzene

Catalytic hydrogenation of nitrobenzene by Ni nanoparticles on supports with high surface area is an economical and green route to produce aniline. To overcome the challenge of Ni nanoparticles blockage in the mesopores of KIT-6, a series of Ni-based KIT-6 catalysts were synthesized by designed engineering approaches. It was found that the engineering approaches were able to tune the nano-ordered of Ni nanoparticles and then remove the blockage on KIT-6, which significantly influence catalytic properties for nitrobenzene hydrogenation. The proposed engineering nano-ordered Ni nanoparticles blockage removal (ENBR) mechanism was systematically characterized. The characterization results confirmed that Ni dispersion, valence and metal surface area were adjusted by the ENBR process. The Ni particles located in the pore were not agglomerated, while the Ni particles located on the surface re-ordered to form larger particles and expose Ni particles blocked in the KIT-6 pores, which is the key factor for the remarkable enhancement of catalytic activity. Among all catalysts, with a specific surface area of 521.4 m2/g and Ni metal surface of 88.2 m2/g, Ni/KIT-6cal+red exhibited the best catalytic activity. This work was promising for the development of supported Ni catalysts to improve catalytic performance by engineering approaches.

Изучение кинетических особенностей синтеза анилина на Ni-содержащем сверхсшитом полистироле

This paper presents a study of the kinetics of catalytic hydrogenation of nitrobenzene to aniline in the presence of Ni-containing catalysts based on super-crosslinked polystyrene. Aniline hydrogenation is a complex multi-stage process accompanied by the formation of a large number of both intermediate and by-products, including azobenzene, azoxybenzene, nitrosobenzene, phenylhydroxylamine and other substances. Therefor the study of the process kinetics is an important scientific and technical task necessary to increase the yield of the target product — aniline. The hydrogenation reaction of nitrobenzene was carried out in a six-cell high-pressure reactor Parr instruments, Series 5000. The products were analyzed by chromatography using a gas chromatograph Kristallux-4000M (Russia, Meta–Chrom). The effect of temperature, pressure, and concentration of the catalyst was studied; optimal reaction conditions were selected that ensure the maximum yield of aniline. Investigation of the effect of the nitrobenzene initial concentration on the rate of its transformation shows that increase of catalyst to nitrobenzene ratio from 0.2 to 0.6 kg (Cat)/kg (NB) leads to a linear increase in the rate of transformation of nitrobenzene from 0.0002 kg (NB) / (kg (Cat)*s ) to 0.0028 kg(NB)/(kg(Cat)*s), a further increase in the ratio of catalyst concentration to nitrobenzene concentration to 1.2 kg (Cat)/kg(NB) leads to stabilization of the nitrobenzene transformation rate at the level of 0.003 kg(NB)/(kg(Cat)*s). An increase in the temperature of the reaction from 90 to 160 °C contributes to a significant increase in the nitrobenzene transformation rate. The constructed dependences made it possible to calculate the apparent activation energy of the process, which amounted to be 50.4 kJ/mol and the preexponential factor, which amounted to be 15821.1 1/s. The applicability of the Langmuir–Henschelwood model to describe the basic kinetic laws of the reaction of catalytic nitrobenzene hydrogenation with the formation of aniline is studied. Numerical methods in the Matlab software allows to determine the values of preexponential factors and activation energies of the nitrobenzene hydrogenation processes, adsorption of nitrobenzene and adsorption of hydrogen, which made it possible to establish the optimal area of nitrobenzene hydrogenation process of hydrogenation of Pн2 = 15–18 atm, C(NB) = 1.2 kg(NB)/kg(Cat), t =115–120 °C providing maximum speed.

Novel cake-like Fe–N–C hybrid for H2 activation

The activation and utilization of hydrogen energy is an effective method to solve the global energy crisis and environmental pollution. Herein, biomass-derived Fe–N–C catalysts for H2 activation were synthesized via the imitation of sponge cake baking. The sample pyrolyzed at 500 °C (Fe–N–C-500) presented the well-defined cake-like architecture with uniform distribution of Fe3O4 nanoparticles (NPs). Doping N species dispersed around metallic NPs in high density. Fe–N–C-500 exhibited excellent performance in the catalytic hydrogenation of nitrobenzene. The activity of Fe–N–C-500 depended on Fe3O4 NPs and pyridinic N, rather than Fe–N. The typical core-shell structure deemed vital for H2 activation in previous reports was not necessary. Notably, water could significantly promote the H2 activation, which might establish the communication between hydrogen molecules adsorbed on Fe3O4 NPs and doping N species through hydrogen bonds. Moreover, low temperature pyrolytic Fe–N–C-500 exhibited excellent stability and provided a promising potential for selective hydrogenation of nitroarenes or alkyne by regulating the reaction condition. This work provides an innovative approach to construct heterogeneous catalysts for H2 activation.

Transformation from 3D Boron Organic Polymers to 1D Nanorod Arrays: Loading Highly Dispersed Nanometal for Green Catalysis.

The increasing global demands for eco-friendly and low-cost catalysts have propelled the advent of nanosized non-noble-metal catalysts to replace traditional noble metals. In this work, ultrafine NiO nanoparticles were prepared rapidly in situ by the strategy of transforming three-dimensional (3D) metal boron organic polymers (BOPs@Ni2+) to one-dimensional (1D) boron organic polymers (BOPs@Ni) nanorod arrays at room temperature. The 3D BOPs@Ni2+ can be quickly obtained by the interaction of 4,4'-bipyridine with Ni2+ and dodecaborate (B12H122-) in an aqueous solution. When Ni2+ is converted into NiO in situ, 1D BOPs@Ni nanostructure transformation from the 3D BOPs@Ni2+ framework was achieved due to the B-H···π interaction between B12H122- and 4,4'-bipyridine. Furthermore, BOPs@Ni exhibits high catalytic activity and rapid kinetics in the conversion of 4-nitrophenol to 4-aminophenol, and the high stability of 1D nanorod arrays guarantees the catalytic activity of BOP@Ni to barely change under recycling for at least 10 times. BOPs@Ni also exhibits good catalytic performance and high selectivity characteristics in the catalytic reduction of a series of nitrobenzene derivatives. This strategy of using BOPs@Ni2+ for loading self-supporting nanometal not only exhibits a highly efficient catalytic hydrogenation of nitrobenzene and its derivative but also provides an effective technical route for designing self-supported nanometal materials.

Beneficial role of the nitrogen-doped carbon nanotubes in the synthesis of the active palladium supported catalyst

The use of nitrogen doped carbon nanotubes (N-CNTs) as a palladium catalyst support resulted in the formation of isolated palladium ions and metal nanoparticles, depending on the Pd content. It was found that the formation of isolated palladium ions is due to the presence of pyridinic nitrogen centers in the N-CNTs and does not depend on the method of palladium deposition (impregnation or reductive deposition). These ions possess high thermal stability in hydrogen atmosphere, poorly adsorb CO even at subambient temperature and are low active in catalytic hydrogenation of nitrobenzene to aniline. The beneficial role of the N-CNTs was found to be in the stabilization by graphitic nitrogen of the metallic Pd nanoparticles of ~1.5 nm size showing high activity towards aniline formation at atmospheric pressure. The possibility of the tailored synthesis of different metal species by means of the N-CNTs as a support opens a wide room for use of these carbon nanomaterials in various catalytic applications.

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.

Core-shell structured Pd catalyst layer encapsulated by polydopamine for a gas-liquid-solid microreactor

In this work, a core-shell structured palladium catalyst layer in a gas-liquid-solid microreactor was proposed for the catalytic nitrobenzene hydrogenation through a facile and efficient approach. Via encapsulating the active palladium cores with the polydopamine shell, the proposed structure can construct barriers between the neighboring nanoparticles to not only inhibit the particle migration and aggregation during the hydrogen reduction and catalytic reaction processes but also protect the active palladium cores from being leaching. Because of these merits, the proposed core-shell structured palladium catalyst layer can significantly intensify the catalysis performance. Experimental results indicated that the developed catalyst layer showed good catalytic activity and operation durability. Compared to the conventional catalyst layer, the core-shell structure exhibited a 120% improvement in terms of the durability. Besides, the effect of the polydopamine encapsulating time on the structure and catalysis performance was also investigated. The best performance was achieved with the encapsulating time of 4 h in the present work. The obtained results reveal a facile and efficient avenue for designing the high-performance microreactors.

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.

The kinetics of catalytic hydrogenation of nitrobenzene in the presence of Ru-containing catalysts

The kinetics of catalytic hydrogenation of nitrobenzene in the presence of Ru-containing catalysts

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.

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.