Selective Hydrogenation Of P-chloronitrobenzene Research Articles

Cu@SiO2 catalyst with high copper dispersion for chemoselective hydrogenation of p-chloronitrobenzene

Selective hydrogenation of p-chloronitrobenzene (p-CNB) is not only of significant industrial importance, but also an important model reaction for selectivity investigation. Despite non-precious metal Cu has been proven to be an effective promoter in bimetallic catalysts, Cu as a single active metal achieving both high conversion and high selectivity are rare reported. In this work, Cu@SiO2 catalysts with high specific surface area (509.8–694.3 m2/g), high Cu dispersion (58.4–69.6 %), and small particle size (2.0–3.0 nm) has been prepared by a simple sol–gel method. The catalysts completely suppress the dechlorination reaction, achieving complete conversion of p-CNB with 99.9 % selectivity for p-chloroaniline (p-CAN). Its microstructure, composition, chemical state, adsorption and reaction behavior have been identified by various conventional ex-situ characterizations of catalysts and in-situ DRIFTs of hydrogenation of p-CNB. Interestingly, even at high loadings, Cu in the catalyst could be highly dispersed, thus exhibiting good catalytic activity. In addition, the Cu catalyst exhibits unique adsorption performance towards p-CNB, which perhaps one of the factors for its good performance. This work not only provides a selective hydrogenation catalyst with high Cu dispersion even at high loading amount by a simple method and but also reveals the importance of the adsorption mode of p-CNB, providing guidance for the development of more efficient catalysts in the future.

Supported Ni0@C[sbnd]N catalyst with dual-reaction surfaces: Structure-performance relation in the selective hydrogenation of p-chloronitrobenzene

How to break the activity-selectivity dependence in halonitrobenzene hydrogenation remains a challenge. In this work, Ni@CN/SiO2 were synthesized and examined in the hydrogenation of p-chloronitrobenzene. It showed that the electron transferred from nitrogen doped carbon shell to Ni0 core (core–shell synergistic effect) dominated the intrinsic activities of Ni@CN/SiO2 with dual-reaction surfaces (H2 dissociated on Ni0 core, while p-chloronitrobenzene was hydrogenated on carbon shell) in the thiophene-free hydrogenation, leading to their higher turnover frequencies than Raney Ni catalyst. During the thiophene-involved hydrogenation, the adsorption of thiophene on Ni0 changed its electron density and blocked the active sites. These enhanced the selectivity, but significantly reduced the activity for Raney Ni catalyst. Comparatively, the carbon shell protected Ni0 core from thiophene adsorption so that the hydrogen dissociated on Ni0 as usual. However, the adsorption of thiophene on the carbon shell reduced the available sites for p-chloronitrobenzene adsorption. Although Ni@CN/SiO2 had lower activities in the thiophene-involved reactions than those of thiophene-free reactions, they achieved ∼100 % p-chloroaniline selectivities and 8-fold higher turnover frequencies than Raney Ni, breaking the activity-selectivity dependence. This reveals that the available sites on the carbon shell and the core–shell synergistic effect determine the thiophene-involved hydrogenation activities of Ni@CN/SiO2 catalysts.

Insight into Single-Atom-Induced Unconventional Size Dependence over CeO2-Supported Pt Catalysts

Summary Identification of the structure-performance relationship at the atomic level is vital for getting a deep understanding of the size-dependence behavior of metal catalysts. Here, an unconventional size dependence of Pt toward selective hydrogenation of p-chloronitrobenzene has been extensively investigated over CeO2 support. An upturned volcanic curve toward the selectivity of p-chloroaniline was found by decreasing the size of Pt from nanoparticles to single atoms. Differences on predominant orbitals among diverse coordination-environment Pt sites were identified to be the key factors influencing the modes of interaction with the C-Cl bond of p-chloroaniline. Specifically, electrostatic repulsion between non-bonding orbitals of Cl and predominant orbitals of Pt sites with high steric hindrance were speculated to be responsible for the suppression of dehalogenation and the high selectivity. This strategy to build correlation between the valence orbitals of active sites and their catalytic behavior could well be expanded to other structure-sensitive reactions and atomically dispersed catalysts.

Pt nanoparticles on Ti3C2Tx-based MXenes as efficient catalysts for the selective hydrogenation of nitroaromatic compounds to amines.

The development of Pt nanocatalysts for the selective hydrogenation of nitroaromatic compounds to the corresponding amines is of great significance to solve the drawbacks associated with a low reserve of Pt. Herein, we develop a protocol for the preparation of a Pt/titanium carbide-based MXene heterostructure for the selective reduction of nitroaromatic compounds. In the heterostructure, well-defined and nano-sized metallic Pt crystallites are uniformly decorated on Ti3C2Tx nanosheets using a mild reducing agent of ammonia borane without additional stabilizing agents. The selective hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CAN) was employed as a model reaction to investigate the catalytic performance of the as-synthesized heterostructure, denoted as Pt/Ti3C2Tx-D-AB. Notably, this catalyst can catalyze the complete conversion of p-CNB to p-CAN with 99.5% selectivity, superior to that of Pt/Ti3C2Tx-D-SB synthesized with sodium borohydride. The high performance of the present catalytic system can be ascribed to the well-dispersed Pt nanoparticles, the abundant surface electron-efficient Pt(0), and the synergistic catalysis between Pt/Ti3C2Tx-D-AB and water. This catalyst also shows generality toward the selective hydrogenation of a series of nitroaromatic compounds to the corresponding amines with high efficiency. The present study provides a strategy to synthesize efficient catalysts for catalytic applications.

Construction the Ni@Carbon nanostructure with dual-reaction surfaces for the selective hydrogenation reaction

Abstract The reduction of the size and modification the surface of Ni0 are generally used to improve the hydrogenation performances of Ni-based catalysts. In this work, a new method derived Ni0@carbon nanostructure was constructed on SiO2 in order to explore an alternative way to improve the intrinsic activity of Ni0 in the selective hydrogenation of p-chloronitrobenzene (p-CNB). The experimental and computational results exhibit that the synergistic effect between Ni0 core and nitrogen-doped carbon shell (Ni0@C-N) can dissociate more hydrogen on larger Ni0 core (~14 nm) than Ni0@C (Ni0 ≈ 11 nm), while the external surface of carbon shell facilitates the oblique adsorption of p-CNB and the consequent hydrogenation. Such formed dual-reaction surfaces inhibit the dechlorination reaction but increase the active hydrogen species. Consequently, Ni0@C-N/SiO2 catalyst (~14 nm) adversely displays ~2.3-fold higher turnover frequency and ~100% p-chloroaniline selectivity, in contrast to Ni0@C/SiO2 (~11 nm) and the commercial Raney Ni (~6 nm) catalysts.

Hierarchical Porosity Tailoring of Sol–Gel Derived Pt/SiO2 Catalysts

Hierarchically porous materials offer the opportunity for catalyst development in regards to improving catalytic performances. In the present work, the combination of latex synthesis, sonochemical reduction and two-step catalysed sol–gel process has been demonstrated to be a versatile method for preparing supported catalysts with tailored hierarchical porosity. This method has been used to prepare porous Pt/SiO2 catalysts with mesopore and macropore size ranges as large as 2–15 nm and 90–400 nm, respectively. These hierarchically porous catalysts presented an excellent catalytic performance for the selective hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CAN). Selectivity values up to 100% at 80% conversion of p-CNB and initial reaction rates up to 74.0 molCNB/min molPt were obtained, while a commercial catalyst exhibited both a lower selectivity of 90.8% and a lower initial reaction rate of 47.7 molCNB/min molPt.

Selective hydrogenation of p-chloronitrobenzene on nanosized gold clusters: A theoretical study

The selective hydrogenation of p-chloronitrobenzene on Au13 and Au55 nanoclusters has been systematically studied by density functional theory (DFT), allowing for a comparison with Au20 nanocluster. All possible adsorption configurations of relevant intermediates are identified. The adsorption energy of all species exhibit the following trend: Au13 > Au20 > Au55. The detailed reaction barriers show that Au55 nanocluster has the least hydrogenation reaction barrier of the rate-limiting step, whereas the dechlorination reaction is least likely to cause on Au55 nanocluster. These observations suggest that the 55-atom gold cluster is predicated to be the appropriate catalyst for practical application.

Morpholine-Modified Pd/γ-Al2O3@ASMA Pellet Catalyst with Excellent Catalytic Selectivity in the Hydrogenation of p-Chloronitrobenzene to p-Chloroaniline

An amino poly (styrene-co-maleic anhydride) polymer (ASMA) encapsulated γ-Al2O3 pellet material has been synthesized successfully. After loading with Pd species and modified with morpholine, the inorganic-organic hybrid material shows an excellent catalytic property in the selective hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CAN). In this procedure, morpholine can connect with the polymer layer in a form of amide bond and acts as an unparalleled immobilized dechlorination inhibitor, which can avoid further dechlorination efficiently and keeps stability due to the repulsive effect from the surviving C-O-C bond. The catalyst as prepared was characterized by using XRD, TGA, SEM, TEM, FT-IR, and ICP-OES, and it was further tested in the selective hydrogenation of p-CNB. It shows a supreme catalytic activity (almost 100%) and selectivity (up to 99.51%) after recycling for even 10 times, much superior to the blank alumina supported palladium (47.09%).

Selective hydrogenation of p-chloronitrobenzene over an Fe promoted Pt/AC catalyst

Selective production of p-chloroaniline from p-chloronitrobenzene without any further hydrogenation products was found feasible by catalytic hydrogenation over the Pt–Fe/AC catalyst.

The Modification of Diphenyl Sulfide to Pd/C Catalyst and Its Application in Selective Hydrogenation of p-Chloronitrobenzene

In this study, diphenyl sulfide (Ph2S) was employed to prepare a series of Ph2S-modified Pd/C catalysts (Pd–Ph2S/C). Catalyst characterization carried out by Brunner–Emmet–Teller (BET), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and CO chemisorption uptake measurements suggested a chemical interaction between Ph2S and Pd. The ligand was preferably absorbed on the active site of Pd metal but after increasing the amount of Ph2S, the adsorption of Ph2S on Pd metal tended to be saturated and the excess of Ph2S partially adsorbed on the activated carbon. A part of Pd atoms without adsorbing any Ph2S still existed, even for the saturated Pd–Ph2S/C catalyst. The Pd–Ph2S/C catalysts exhibited a good selectivity of p-chloroaniline (p-CAN) in the hydrogenation of p-chloronitrobenzene (p-CNB). However, the chemisorption between Ph2S and Pd was not so strong that part of Ph2S was leached from Pd–Ph2S/C catalyst during the hydrogenation, which caused the decline of the selectivity of p-CAN over the used Pd–Ph2S/C catalyst. Resulfidation of the used Pd–Ph2S/C catalyst was effective to resume its stability, and the regenerated Pd–Ph2S/C catalyst could be reused for at least ten runs with a stable catalytic performance.

Effective Hydrogenation of p-Chloronitrobenzene over Iridium Nanoparticles Entrapped in Aluminum Oxy-Hydroxide under Mild Conditions

The Ir/AlO(OH) catalyst was prepared by sol-gel method and used for selective hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroniamine (p-CAN). The mechanism of p-CNB hydrogenation over the catalyst was discussed. The hydrogen bond between the surface hydroxyl groups of the catalyst and the nitrogen present in p-CNB facilitated the hydrogenation of nitro group. On the other hand, the formation of hydrogen bond between the hydrogenation product and water promotes the rapid desorption of the hydrogenation product on the surface of the catalyst. Thus the activity and selectivity were greatly promoted.

Poly(Vinylpyrrolidone)-Anchored Iridium Nanoparticles Supported on Al<sub>2</sub>O<sub>3</sub> as Ultra-Selective Catalyst for the Hydrogenation of <i>p</i>-Chloronitrobenzene

Poly (vinylpyrrolidone)-anchored iridium nanoparticles (PVP-Ir) were prepared via the reduction of H2IrCl6·nH2O in ethanol/water mixtures. The catalytic properties of the colloidal nanoparticles that dispersed on Al2O3(PVP-Ir/Al2O3) were investigated in the selective hydrogenation ofp-chloronitrobenzene (p-CNB) top-chloroaniline (p-CAN). The results indicated that the selectivity top-CAN remained on the level of 100 % at complete conversion ofp-CNB at lower temperature of 288 K. Moreover, the side reaction of hydrogenolysis of the carbon-halogen bond was completely inhibited in the absence of promoters and inhibitors. The great improvement on activity and selectivity of PVP-Ir/Al2O3was attributed to the highly and homogeneously dispersion of the iridium nanoparticles on the support Al2O3and the addition of appropriate amount of water in organic solvents

Chemoselective hydrogenation of nitroarenes: Boosting nanoparticle efficiency by confinement within highly porous polymeric framework

We report for the first time 99.9% yield of aminocompounds and high TOFs (up to 61s−1) in the liquid-phase hydrogenation of several para-substituted (–OH, –OCH3, –CH3, –H, –Br, –Cl, –COOH and –NO2) nitroaromatics over quasi-monodispersed (ca. 3.3nm from microscopy and CO chemisorption) Pt nanoparticles (NPs) confined within a hyper cross-linked polystyrene (HPS) polymeric matrix (uniform pore size ∼4.6nm; 1065m2g−1). Taking the selective hydrogenation of p-chloronitrobenzene as a model reaction, an antipathetic structure sensitivity (i.e. up to a 3-fold TOF greater over larger, 1.6→3.3nm, Pt NPs) has been established. Moreover, a higher activity and amine selectivity were attained at elevated pressures (1→20bar) irrespective of the support (i.e. active carbon, Al2O3 and HPS). Nonetheless, while Pt/HPS shows high stability without any activity/selectivity loss in repeated reaction runs, the state-of-the-art active carbon and alumina-supported Pt catalysts underwent a decrease in activity as a result of metal leaching. Our results demonstrate the potential of HPS as a suitable support for tailoring metal nanoparticle size and circumvent undesirable metal leaching.

Effect of rare earths on selective hydrogenation of p-chloronitrobenzene over PtMOx/CNTs catalysts

The effect of rare earths (Sm, Pr, Ce, Nd and La) on the hydrogenation properties of p-chloronitrobenzene (CNB) over Pt/CNTs catalyst was studied in ethanol at 303 K and normal pressure. The results exhibited that the hydrogenation of p-CNB could be carried out over PtMOx/CNTs catalysts. Both catalytic activities and yields of p-chloroaniline (CAN) were all improved. PtCeOx/CNTs catalyst exhibited the best catalytic activity (TOF was 0.47 s −1) and the highest yield of p-CAN (97.5 mol%). PtCeOx/CNTs (1.0 wt%) catalyst exhibited good stability on the hydrogenation of p-CNB.

Selective hydrogenation of p-chloronitrobenzene over Ni–P–B amorphous catalyst and synergistic promoting effects of B and P

Ni–P–B amorphous alloy catalyst was prepared by chemical reduction of Ni 2+ with KBH 4 and NaH 2PO 2 as co-reducing agents. During liquid-phase hydrogenation of p-chloronitrobenzene ( p-CNB), Ni–P–B exhibited higher activity and better selectivity to p-chloroaniline ( p-CAN) than either Ni–B or Ni–P, obviously owing to the synergistic promoting effects of both the P and the B co-alloying with the metallic Ni. The P promoted hydrogenation activity via enhancing the intrinsic activity ( R H S ) since the Ni active sites alloying with P became more highly unsaturated, which could adsorb hydrogen more strongly, taking into account that p-CNB hydrogenation was first-order with respect to hydrogen. The B promoted hydrogenation activity via enhancing the dispersion degree of Ni active sites. The higher selectivity to p-CAN could be attributed to the inhibition of hydrodehalogenation since the metallic Ni alloying with P could adsorb the nitro group preferentially against the chlorine atom in p-CNB. Meanwhile, the presence of the alloying B could further enhance the adsorption strength for nitro group via side-bonding and also protected Ni active sites from poisoning by the amine resulting from p-CNB hydrogenation.

Selective Hydrogenation of p-Chloronitrobenzene over Ru–Ir/γ-Al2O3 Catalyst Modified by Organic Amines

Abstract A Ru–Ir/γ-Al2O3 bimetallic catalyst was prepared by impregnating γ-Al2O3 with an isopropylalcohol solution of RuCl3 and H2IrCl6. The effect of organic amine modifiers on the selective hydrogenation of p-chloronitrobenzene (p-CNB) over Ru–Ir/γ-Al2O3 was investigated. The addition of ethylenediamine and L-lysine remarkably improved the catalytic activity of Ru–Ir/γ-Al2O3 and the selectivity for p-chloroaniline (p-CAN) at high conversion of p-CNB. In the presence of ethylenediamine, the conversion of p-CNB increased from 37.2% to 95.6% and the selectivity for p-CAN was maintained at 100%. Similarly, the addition of L-lysine greatly enhanced the activity of the catalyst and completely suppressed the formation of by-products. The promotion effect was attributed to the coordination of ethylenediamine or L-lysine with the metal center, which improved the cooperation between ruthenium and iridium.

Expanded graphite applied in the catalytic process as a catalyst support

An amorphous NiB supported on expanded graphite (EG) catalyst was prepared as an example to show the superior characteristics of EG as a novel carbon support material. EG and the prepared catalysts were characterized by mercury porosimetry, inductively coupled plasma spectrometer (ICP), scanning electronic microscopy (SEM), transmission electron microscope (TEM) and selected area electron diffraction (SAED). The catalytic activities of prepared catalysts were investigated by the hydrogenation of sulfolene to sulfalone and the selective hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CA). We showed that the prepared Ni-B/EG catalyst exhibited very high catalytic activity.

Pt/γ-Al2O3 catalytic membranes vs. Pt on γ-Al2O3 powders in the selective hydrogenation of p-chloronitrobenzene

The catalytic activity of Pt/γ-Al2O3 membrane reactors, prepared using mesitylene solvated platinum atoms as source of active Pt particles, has been compared with that of analogously obtained Pt/γ-Al2O3 powders in the liquid phase hydrogenation of p-chloronitrobenzene. A largely different behaviour has been observed, the membrane reactor acting as a H2 richer system.

A remarkable synergic effect of polymer-anchored bimetallic palladium–ruthenium catalysts in the selective hydrogenation of p-chloronitrobenzene

A synergic effect of the polymer-anchored bimetallic palladium-ruthenium catalysts can lead to a remarkable increase in the selectivity for p-chloroaniline in the selective hydrogenation of p-chloronitrobenzene under atmospheric pressure and in the presence of a small amount of base.