Hydrogenation Of Chloronitrobenzene Research Articles

Yeast-derived N, P co-doped porous green carbon materials as metal-free catalysts for selective hydrogenation of chloronitrobenzene

The N, P co-doped porous carbon materials were synthesized via the in situ pyrolysis of yeast post-water treatment and exhibited superior nitro hydrogenation performance using molecular hydrogen and hydrazine hydrate as hydrogen sources.

Bimetallic and trimetallic Pt-based catalysts for selective hydrogenation of p-chloronitrobenzene to p-chloroaniline

The selective hydrogenation of p-chloronitrobenzene (p-CNB) is a crucial step in the preparation of p-chloroaniline (p-CAN). However, the competitive reactions of NO2 hydrogenation and C-Cl hydrogenolysis make it challenging to inhibit the undesired dechlorination side reaction during this process. Herein, we developed a series of bimetallic PtM/γ-Al2O3 (M = Co, Cu, Ni, Fe, Zn, Ga, and Sn) and trimetallic PtCuCox/γ-Al2O3 catalysts to enhance the selectivity of p-CAN and suppress the formation of aniline (AN). Among the bimetallic catalysts, PtCo/γ-Al2O3 showed the highest hydrogenation activity due to its high electron-rich degree of Pt. Conversely, PtCu/γ-Al2O3 displayed the highest p-CAN selectivity and the lowest AN selectivity, primarily owing to the presence of electron-deficient Pt. Remarkably, the trimetallic PtCuCo/γ-Al2O3 catalyst exhibited superior hydrogenation performance, achieving 97.3 % p-CAN selectivity and 0.4 % AN selectivity at complete conversion of p-CNB, while maintaining good stability over five cycles. This enhancement was attributed to the synergistic effect among Pt, Cu and Co. To further investigate the effect of support, we prepared bimetallic PtM3 (M = Co, Cu, Ni and Zn) catalysts supported on reducible CeO2. Interestingly, the use of CeO2 as a support facilitated the condensation path from p-CNB to p-CAN via azobenzene compounds, distinct from the direct path observed with γ-Al2O3 support. Furthermore, the AN selectivity on all PtM3/CeO2 was less than 1 %, indicating effective inhibition of dechlorination reactions. This study highlights the importance of a multi-metal synergistic strategy and the effect of the support to achieve superior performance in chloronitrobenzene hydrogenation.

Solvent free continuous hydrogenation of chloronitrobenzene over Pt/amide group grafted AC catalysts

Solvent-free hydrogenation of chloronitrobenzene is considered as the most efficient and cleanest method for the production of chloroanilines which are important intermediates in the medicine, pigment and dye industry. However, it is difficult to suppress the side reaction of dechlorination in the solvent-free hydrogenation process. Herein, a novel Pt /amide group grafted AC catalyst was prepared by covalently grafting N-containing groups on commercial activated carbon which forms amide bond for solvent-free hydrogenation of chloronitrobenzene. Several Pt /amide group grafted AC catalysts grafted with different N-containing groups were prepared and experimental results indicate that Pt /amide group grafted AC catalysts covalently grafted with 1,3-cyclohexanediamine exhibit excellent performance on the suppression of dechlorination. The characterization results reveal that Pt/C catalyst grafted with 1,3-cyclohexanediamine has a narrower particle size distribution and smaller average size in comparison with Pt/C. The catalyst was evaluated in the solvent-free continuous hydrogenation of o-CNB to o-CAN and no dechorinated products was detected and high yield of o-CAN (more than 99.9%) was obtained in the range of 50∼120 ℃ compared with the severe dechlorination using Pt/C catalyst (yield of dechlorinated products≥70%). Additionally, no catalyst deactivation was observed in 200 h and turnover number per mole active metal (12290) is higher than the catalysts reported in the literatures (364∼9280) exhibiting the remarkable stability of Pt/C-N catalyst.

Low loading Pt on TiO2 for the ultra‐selective hydrogenation of chloronitrobenzenes to chloroanilines

AbstractLow loading Pton TiO2 were prepared by an impregnation‐reduction process for chemoselective hydrogenation of chloronitrobenzenes (CNBs) to chloroanilines (CANs). The structure and physicochemical properties were characterized by N2 adsorption‐desorption, X‐ray diffraction, high resolution transmission electron microscopy, X‐ray photoelectron spectroscopy and temperature programmedreduction. The low loading Pt(≤0.08 wt %) on TiO2 exhibited outstanding chemoselectivity for the catalytic hydrogenation of CNBs to CANs, without any disturbance on carbon‐chlorine bond. The characterization data suggested that the Pt particles were highly dispersed on TiO2 and strongelectronicinteractionsoccur between the dispersedPt andTiO2support, which led toelectron deficiency of nearly all Pt and production of suboxide TiOx species (x<2) in the 0.08 wt % Pt/TiO2. The electron‐deficient Pt and suboxide TiOx species favor N=O bondactivation, leading to its unique chemoselectivity.

Nano porous PtRu alloy catalyst with enhanced synergic effect for selective hydrogenation of chloronitrobenzene

Selective hydrogenation of chloronitrobenzene (CNB) to chloroaniline (CAN) is a critical reaction for producing multiple valuable fine chemicals. Inhibiting the dechlorination is extremely vital for this reaction. In this work, we synthesize supported nano porous PtRu alloy catalyst for this catalytic reaction. The special structure of alloy catalyst, mutual-accessible Ru enriched surface and Pt enriched core, strengthens the synergic effect between Ru and Pt, thus improves the catalytic performance. As a result, 100% of o-chloronitrobenzene (o-CNB) conversion and 99.9% of o-chloroaniline (o-CAN) selectivity are achieved by the most optimal catalyst. Besides, the catalyst shows superior selectivity of o-CAN (98%) even under harsh reaction conditions such as high temperature of 150 °C and high pressure of 6 MPa. The excellent catalytic performance is also observed in selective hydrogenation of m-chloronitrobenzene (m-CNB) and p-chloronitrobenzene (p-CNB) as well.

Hybrid Nanostructure Catalyst with Low Loading of Pt for the High-Efficiency Catalytic Hydrogenation of Chloronitrobenzene.

Fabrication of low-loading, noble-metal, stable, and high-performance metal catalysts remains a thorny issue. Herein, we demonstrate the successful formation of a hybrid nanostructure Pt/TiO2/SBA-15 catalyst (denoted as HNSC-P/T/S; Pt, 0.09%; TiO2, 10%) with satisfactory activity in the hydrogenation of para-chloronitrobenzene (p-CNB). The HNSC-P/T/S showed >99% conversion and a high selectivity of >98%, and the turnover frequency number (TOF) reached 66 766 h-1, which was impossible to achieve with Pt/TiO2 (denoted as P/T) or Pt/SBA-15 (denoted as P/S). The success of the catalytic activity of the HNSC-P/T/S mainly relies on its synergistic effect and special structure, which can fully develop the catalytic ability of Pt, thereby reducing the Pt loading in the noble-based catalyst. Furthermore, the HNSC-P/T/S could also achieve an excellent catalytic activity in the hydrogenation of other nitroarenes. Hence, this work proposes a direction to prepare a noble-based catalyst with a low loading of noble metals for diverse applications.

Palladium Nanoparticles Inset into the Carbon Sphere with Robust Acid Resistance for Selective Hydrogenation of Chloronitrobenzene

Palladium Nanoparticles Inset into the Carbon Sphere with Robust Acid Resistance for Selective Hydrogenation of Chloronitrobenzene

Nano Porous Ptru Alloy Catalyst with Enhanced Synergic Effect for Selective Hydrogenation of Chloronitrobenzene

Nano Porous Ptru Alloy Catalyst with Enhanced Synergic Effect for Selective Hydrogenation of Chloronitrobenzene

Pre-Coking Strategy Strengthening Stability Performance of Supported Nickel Catalysts in Chloronitrobenzene Hydrogenation

Supported nickel catalysts represent a class of important catalytic materials in selective hydrogenations, but applications are frequently limited by metal agglomeration or active-site blocking induced by the presence of hydrogen halides. Herein, we report a novel pre-coking strategy, exposing the nickel nanoparticles under methane dry reforming conditions to manipulate performance in the continuous-flow hydrogenation of 1,2-dichloro-4-nitrobenzene. Compared with the pristine nickel catalyst, the nanotube-like coke-modified nickel catalyst showed weakened hydrogenating ability, but much improved stability and slightly better selectivity to the target product, 3,4-dichloroaniline. Characterization results revealed that the strengthened stability performance can be mainly linked to the reduced propensity to retain chlorine species, which seems to block the access of the substrate molecules to the active sites, and thus is a major cause of catalyst deactivation on the pristine nickel catalyst. Coke deposition can occur on the pre-coked nickel catalyst but not on the pristine analog; however, the impact on the stability performance is much milder compared with that on chlorine uptake. In addition, the presence of coke is also beneficial in restraining the growth of the nickel nanoparticles. Generally, the developed method might provide an alternative perspective on the design of novel transition-metal-based catalytic materials for other hydrogenation applications under harsh conditions.

Synergistic catalysis by a hybrid nanostructure Pt catalyst for high-efficiency selective hydrogenation of nitroarenes

A hybrid nanostructure Pt/@-ZrO2/SBA-15 catalyst was fabricated by coating ZrO2 on SBA-15 (ZrO2/SBA-15), and then loaded Pt nanoparticles on the ZrO2/SBA-15 by a photochemical route at room temperature. This catalyst demonstrated outstanding activity and excellent selectivity (>99%) for hydrogenation of nitroarenes, outperforming conventional catalysts (Pt/SBA-15, Pt/ZrO2, Pt/AC, Pt/Al2O3, and Pt/SiO2). For the hydrogenation of chloronitrobenzene, the Pt/@-ZrO2/SBA-15 catalyst achieved a turnover frequency (TOF) of 2.5–7.5 s−1. Particularly, the 0.07%Pt/@-ZrO2/SBA-15 catalyst yielded a TOF as high as 12 s−1 in the hydrogenation of nitrobenzene, much higher than the single-atom 0.08%Pt/FeOx-R200 (0.67 s−1) catalyst reported in the literature. Unlike single-atom (low metal loading) or conventional catalysts (high metal loading), this hybrid nanostructure catalyst with high or low Pt loading showed high activity. Moreover, the Pt/@-ZrO2/SBA-15 catalyst exhibited excellent recyclability; the catalytic activity did not decrease after six reaction cycles. The extraordinary activity and selectivity of this catalyst are attributed to the special structure and the synergistic effect. The catalysts also deliver high catalytic activity and selectivity for nitroarenes with various reducible substituents into the corresponding aminoarenes. Our findings provide a new perspective on developing a high-efficiency hybrid nanostructure catalyst for a variety of catalytic reactions.

Non-Noble Metal Ni Nanoparticles Supported on Highly Dispersed TiO2-Modified Activated Carbon as an Efficient and Recyclable Catalyst for the Hydrogenation of Halogenated Aromatic Nitro Compounds under Mild Conditions

TiO2-modified oxygen-functionalized activated carbon (TiO2@OAC)-loaded nickel-based catalysts (Ni/TiO2@OAC) were synthesized and applied in the hydrogenation of chloronitrobenzene (CNB) to chloroan...

Preparation and Catalytic Performance of Metal-Rich Pd Phosphides for the Solvent-Free Selective Hydrogenation of Chloronitrobenzene

A facile synthesis method of palladium phosphide supported on the activated carbon was developed. The effects of Pd precursors for phosphatization, phosphatization temperature, and the ratio of hypophosphite/Pd on the generation of palladium phosphide were investigated, and a generation mechanism of the Pd3P crystal structure is proposed. The results demonstrate that only PdO, rather than Pd or PdCl2, can transform into Pd phosphide without damage to the activated carbon. The penetration of P into the Pd particle can dramatically improve the dispersion of Pd species particles on the activated carbon. The generation of Pd phosphide greatly depends on the phosphatization temperature and the ratio of hypophosphite/Pd. An intact Pd3P crystal structure was obtained when the ratio of hypophosphite/Pd reached 32 and the phosphatization temperature was above 400 °C. The Pd3P supported on the activated carbon exhibited superior catalytic performance in terms of the hydrogenation of halonitrobenzenes to haloanilines because it had few L acids and B acids sites and could not generate deficient-electron active hydrogen atoms as electrophiles.

Construction of Pd-M (M = Ni, Ag, Cu) alloy surfaces for catalytic applications

The fabrication of ultrathin alloy shells as heterogeneous catalysts to increase the utilization efficiency and enhance the catalytic activity of metal atoms has been recognized as an effective method for the construction of efficient metal nanocatalysts, particularly noble-metal nanocatalysts. In this study, we demonstrate the successful formation of Pd-M (M = Ni, Ag, Cu) alloy shells with a tunable thickness on preformed nanoscale Pd seeds. The success of this synthesis mainly relies on the combination of the slow reduction of “M” ions and the subsequent diffusion of M ad-atoms into the surface lattice of Pd seeds. The composition of the Pd-M alloy shell is easily tuned by changing the type and amount of the added precursor, and the shell thickness is manipulated according to the reaction time. More significantly, the surface structure of these alloy shells is maintained after the reaction, implying that any desired surface structure of Pd-M alloy shells can be prepared by using the appropriate starting materials. Further catalytic evaluation of the hydrogenation of chloronitrobenzenes shows that these alloy surfaces exhibit significantly improved selectivity compared to the Pd seeds. The Pd-Ni alloy surfaces exhibit much better catalytic selectivity (as high as > 99%) than Pd catalysts.

Direct synthesis of Pd incorporated in mesoporous silica for solvent-free selective hydrogenation of chloronitrobenzenes

Pd incorporated in mesoporous silica (Pd-MS) catalysts were prepared by a direct synthesis method in the presence of 1, 3, 5-trimethylbenzene (TMB) and their formation mechanism was proposed. TMB not only acted as an effective expanding agent to enlarge pore size and pore volume of MS but also acted as a structure-directing agent to induce the formation of worm-like morphology. For solvent-free hydrogenation of p-chloronitrobenzene (p-CNB), a complete conversion of p-CNB with a selectivity towards p-chloroaniline of 99.9% over the Pd-MS catalyst with addition of TMB (Pd-MS-50-TMB, where 50 represented the addition of 5mL of aqueous NH3) was obtained at 85°C and 3.45MPa of H2 in 2h, while only 48.4% p-CNB conversion over Pd-MS-50 synthesized without TMB was obtained. The enhanced activity of the Pd-MS-50-TMB was not only attributed to the smaller size of Pd particles, but also to the worm-like morphology of the support with larger pore size and pore volume that could enhance mass transfer and allow the reactants more facile access to Pd for reaction.

Preparation of gold-containing binary metal clusters by co-deposition-precipitation method and for hydrogenation of chloronitrobenzene

Nano-gold catalyst has been reported to have high activity and selectivity for liquid phase hydrogenation reaction. In this study, gold-containing bimetals were loaded on TiO2. For bimetallic catalysts, gold and different metals were prepared by the deposition-precipitation method, and then used NaBH4 to reduce metal cations. The catalysts were characterized by X-ray diffraction, transmission electron microscopy, high resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The catalytic properties of these catalysts were tested by hydrogenation of p-chloronitrobenzene (p-CNB) in a batch reactor at 1.1 MPa H2 pressure, 373 K and 500 rpm. Cu, Ag, Ru, and Pd formed nano-alloy with Au. In addition, Cu–Au, Ag–Au, and Ru–Au alloy had Cu-, Ag-, and Ru-enriched surface, respectively. Instead, Pd–Au alloy had Pd-enriched surface. There are two kinds of alloy effects: (1) geometric effects, i.e., the surface-enriched metal would change the distance of Au–Au atoms that is required for facilitating the hydrogenation of chloronitrobenzene; and (2) electronic effects, which involve charge transfer between the metals. The activity decreased in the following order: PdAu/TiO2 > Au/TiO2 > NiAu/TiO2 > AgAu/TiO2 > RuAu/TiO2 > CuAu/TiO2. Comparing with other metals, adding Pd in Au showed a higher activity. Adding palladium could reduce gold-valence state, and increased active sites for reaction.

Factors determining the chemoselectivity of phosphorus-modified palladium catalysts in the hydrogenation of chloronitrobenzenes

The precursor nature effect on the state of the Pd–P surface layer in palladium catalysts and on their properties in the liquid-phase hydrogenation of chloronitrobenzenes under mild conditions has been investigated. A general feature of the Pd–P-containing nanoparticles obtained from different precursors and white phosphorus at P/Pd = 0.3 (PdCl2 precursor) and 0.7 (Pd(acac)2 precursor) is that their surface contains palladium in phosphide form (BE(Pd3d 5/2) = 336.2 eV and BE(Р2р) = 128.9 eV) and Pd(0) clusters (BE(Pd3d5/2) = 335.7 eV). Factors having an effect on the chemoselectivity of the palladium catalysts in chloronitrobenzenes hydrogenation are considered, including the formation of small palladium clusters responsible for hydrogenation under mild conditions.

Preparation of a magnetically recoverable nanocatalyst via cobalt-doped Fe3O4 nanoparticles and its application in the hydrogenation of nitroarenes

In this paper, we describe the facile and effective preparation of a series of cobalt-doped Fe3O4 nanocatalysts via chemical coprecipitation in an aqueous solution. The catalyst allowed the hydrogenation of chloronitrobenzenes to chloroanilines (CAs) to proceed at low temperatures in absolute water and at atmospheric pressure, resulting in approximately 100% yield and selectivity. Several factors that influence the yield of CAs were investigated. The results showed that the suitable dosage of the catalyst was ~10 mol.% of the substrate, and the optimal reaction time, reaction temperature, and reaction pressure were 20 min, 80 °C, and atmospheric pressure, respectively. Under the optimal reaction conditions, the CA yield was as high as 98.4%, and the nitro reduction rate reached 100%, which indicates the excellent selectivity of the homemade catalyst. This process also overcomes the environmental pollution harms associated with the traditional process.

Effect of loading method on selective hydrogenation of chloronitrobenzenes over amorphous Ni–B/CNTs catalysts

Carbon nanotubes (CNTs)-supported amorphous Ni–B catalysts were prepared by selectively depositing Ni–B particles inside or outside the CNTs (Ni–B-in/CNTs or Ni–B-out/CNTs). Hydrogenation of chloronitrobenzenes was carried out to test how the Ni–B particle-loading method over the CNTs affected the catalytic performance. Compared with the Ni–B-out/CNTs, the Ni–B-in/CNTs, because of the nanospace limitation inside the CNTs, restricted the size and aggregative behavior of the Ni–B particles better, and formed an amorphous Ni–B alloy with high thermal stability. The Ni–B-in/CNTs exhibited a much higher catalytic activity for hydrogenation of chloronitrobenzenes than the Ni–B-out/CNTs.

Highly efficient and selective hydrogenation of chloronitrobenzenes to chloroanilines by H2 over confined silver nanoparticles

The Ag NPs with sizes ranging form 5–6 nm confined into SBA-15 show a very good activity and robust recycle ability for hydrogenation of chloronitrobenzenes to the corresponding chloroanilines by H2, comparing with that of the traditional SiO2 supported Ag catalysts.

Effect of the Carbon Support on the Catalytic Activity of Ruthenium‐Magnetite Catalysts for p‐Chloronitrobenzene Hydrogenation

AbstractFew‐layer graphene, carbon nanotubes, and N‐doped carbon nanotubes have been used to support Ru and/or Fe3O4 nanoparticles. The materials were prepared by a new single‐step sustainable method that involves: 1) a simple procedure, 2) the use of propanol as a solvent, 3) short reaction times, 4) an efficient and energy‐saving heat source, and 5) the absence of any high‐boiling‐point stabilizing agent or organic surfactant. The supported nanoparticles were characterized by TEM, XRD, inductively coupled plasma optical emission spectroscopy, and SQUID magnetometer analyses and employed in the selective hydrogenation of p‐chloronitrobenzene to p‐chloroaniline with very promising results. The hydrogenation runs evidence the marked influence of the diverse carbon nanostructures on the reaction rate, and highlights the promising activity of nanocatalysts supported on few‐layer graphene.