Hydrogenation Of P-chloronitrobenzene Research Articles

Decoupling the electronic and geometric effects of Pt catalysts in selective hydrogenation reaction

Decoupling the electronic and geometric effects has been a long cherished goal for heterogeneous catalysis due to their tangled relationship. Here, a novel orthogonal decomposition method is firstly proposed to settle this issue in p-chloronitrobenzene hydrogenation reaction on size- and shape-controlled Pt nanoparticles (NPs) carried on various supports. Results suggest Fermi levels of catalysts can be modulated by supports with varied work function (Wf). And the selectivity on Pt NPs of similar size and shape is linearly related with the Wf of support. Optimized Fermi levels of the catalysts with large Wf weaken the ability of Pt NPs to fill valence electrons into the antibonding orbital of C–Cl bond, finally suppressing the hydrodehalogenation side reaction. Foremost, the geometric effect is firstly spun off through orthogonal relation based on series of linear relationships over various sizes of Pt NPs reflecting the electronic effect. Moreover, separable nested double coordinate system is established to quantitatively evaluate the two effects.

In Situ Transformation of ZIF-8 into Porous Overlayer on Ru/ZnO for Enhanced Hydrogenation Catalysis.

Supported metal catalysts play a significant role in heterogeneous catalysis in liquid phase reaction systems, but they usually suffer from a stability problem. Encapsulation of active metal species without the compromise of catalytic performance has been considered as an effective strategy. Here, we report an ultrastable Ru-based catalyst with particle size of around 1.1 nm for selective hydrogenation reaction. The highly dispersed Ru species are covered by the in situ formed porous N-C-ZnO overlayer, which is induced through the transforming of ZIF-8 shell that derives from a ZnO substrate. The resulting Ru/ZnO@N-C-ZnO catalyst can exhibit good stability in the hydrogenation of p-chloronitrobenzene after 20 cyclic runs with 100% selectivity toward p-chloroaniline. Comparatively, the naked Ru/ZnO catalyst with larger Ru particles shows serious metal leaching issue with inferior stability and poor selectivity. It is revealed that the excellent performance of Ru/ZnO@N-C-ZnO is attributed to the porous overlayer, which strengthens the bonding of Ru nanoparticles on ZnO.

Ru@Carbon Nanotube Composite Microsponge: Fabrication in Supercritical CO2 for Hydrogenation of p-Chloronitrobenzene.

Novel heterogeneous catalysts are needed to selectively anchor metal nanoparticles (NPs) into the internal space of carbon nanotubes (CNTs). Here, supercritical CO2 (SC-CO2) was used to fabricate the Ru@CNT composite microsponge via impregnation. Under SC-CO2 conditions, the highly dispersive Ru NPs, with a uniform diameter of 3 nm, were anchored exclusively into the internal space of CNTs. The CNTs are assembled into a microsponge composite. The supercritical temperature for catalyst preparation, catalytic hydrogenation temperature, and time all have a significant impact on the catalytic activity of Ru@CNTs. The best catalytic activity was obtained at 100 °C and 8.0 MPa: this gave excellent selectivity in the hydrogenation of p-chloronitrobenzene at 100 °C. This assembly strategy assisted by SC-CO2 will be promising for the fabrication of advanced carbon composite powder materials.

Efficient and recyclable bimetallic Co–Cu catalysts for selective hydrogenation of halogenated nitroarenes

Silica supported N-doped carbon layers encapsulating Co–Cu nanoparticles (Co1Cux@CN/SiO2) were prepared by a one-step impregnation of Co(NO3)2·6H2O, Cu(NO3)2·3H2O, urea and glucose, following in situ carbothermal reduction. Effects of Cu contents on the catalytic performance of the Co1Cux@CN/SiO2 catalysts were investigated for selective hydrogenation of p-chloronitrobenzene to p-chloroaniline. The Co1Cu0.30@CN/SiO2 with Cu/Co molar ratio of 0.30:1 presented much higher activity and stability than the monometallic Co@CN/SiO2 catalyst. The addition of Cu into Co1Cux@CN/SiO2 catalysts had favorable effects on the formation of highly active Co–N sites and N-doped carbon layer. The role of the N-doped carbon layer was to protect the Co from oxidation by air, and the Co1Cu0.30@CN/SiO2 could be reused for at least 12 cycles without decrease in catalytic efficiency. Mechanistic and in situ infrared studies revealed that the interaction effect between the Co and Cu atoms made the surface of Co highly electron rich, which decreased adsorption of halogen groups and resulting in the enhanced selectivity during chemoselective hydrogenation of halogenated nitroarenes for a wide scope of substrates.

Controlled synthesis of dendritic ruthenium nanostructures under microwave irradiation and their catalytic properties for p-chloronitrobenzene hydrogenation

In this study, the shape-controlled synthesis of ruthenium (Ru) nanostructures was examined using microwave irradiation. Dendritic Ru nanostructures, with an average diameter of about 34.7 nm, were successfully synthesized when ruthenium chloride (RuCl3) was reduced using a reducing agent of benzyl alcohol, in the presence of polyvinylpyrrolidone (PVP) under microwave irradiation for 360 s. By examining selected parameters affecting the shape-controlled synthesis of dendritic Ru nanostructures, i.e., the concentration of the RuCl3 precursor, different reducing agents, molecular weight of PVP and the molar ratio of RuCl3/PVP, were identified as key factors affecting the successful synthesis of dendritic Ru nanostructures. The catalytic performance of obtained dendritic Ru nanostructures was evaluated for hydrogenation of p-chloronitrobenzene (p-CNB). High selectivity to p-chloroaniline (p-CAN) of about 99.58% was obtained using dendritic Ru nanostructure catalysts at 80 °C under 1 MPa hydrogen pressure, having a 72.81% conversion rate of p-CNB. The selectivity to p-CAN with a dendritic Ru nanostructure catalyst is notably higher than that of conventional 5% ruthenium/carbon catalysts (62.12%). Here in we demonstrate that synthesized dendritic Ru nanostructures present a promising catalytic performance in the hydrogenation of p-CNB, having potential applicability to a wide range of catalytic reactions.

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.

Pt/Al2O3 coated with N-doped carbon as a highly selective and stable catalyst for catalytic hydrogenation of p-chloronitrobenzene to p-chloroaniline.

Selective catalytic hydrogenation of p-chloronitrobenzene on Pt-based catalysts is a green and high-efficient way for p-chloroaniline production. However, supported monometallic Pt catalysts often exhibit undesirable p-chloroaniline selectivity. We herein reported supported Pt catalysts with N-doped carbon (NC) as an overcoating (Pt/Al2O3@NC) to overcome the disadvantage. Three Pt/Al2O3@NC catalysts with different NC coating amounts were prepared by in situ carbonization of an ionic liquid. For comparison, Al2O3 coated by NC and Pt/Al2O3 coated by SiO2 were also prepared. A combination characterization confirmed that the NC overcoating was successfully formed on Pt/Al2O3 surface and Pt particles were completely coated by NC layers when ion liquid amount increased to 25 μl per g catalyst. Due to the intimate contact of NC layers and Pt particles Pt-NC heterojunctions were effectively formed on the catalyst surface. For the catalytic hydrogenation of p-chloronitrobenzene, Pt/Al2O3@NC with 25 μl ionic liquid as the NC precursor exhibited 100% selectivity to p-chloroaniline at 100% conversion of p-chloronitrobenzene. A lower ionic liquid amount led to decreased selectivity to p-chloroaniline. Furthermore, no deactivation was observed on Pt/Al2O3@NC during 5 catalytic cycles. The findings in the study demonstrate that coating noble metal catalysts by N-doped carbon is a promising method to enhance the selectivity and stability for catalytic hydrogenation of p-chloronitrobenzene.

Highly active and selective catalytic hydrogenation of p-chloronitrobenzene to p-chloroaniline on Pt@Cu/TiO2

It is still a great challenge to achieve trade-off between catalytic activity and selectivity on supported Pt catalysts for the catalytic hydrogenation of p-chloronitrobenzene. Here through a two-step photodeposition method, bimetallic Pt@Cu/TiO2 catalysts with different Cu contents were synthesized to deal with this problem. For comparison, Pt/TiO2 and Cu/TiO2 were also synthesized using the photodeposition method. Characterization results suggested that Cu was site-specifically deposited on Pt particle surface and core-shell nanocomposites with Pt as core and Cu as shell were formed on TiO2. Additionally, electron transfer between Pt and Cu occurred in bimetallic nanoparticles, resulting in negatively charged Pt and positively charged Cu. For the catalytic hydrogenation of p-chloronitrobenzene, Pt/TiO2 exhibited the highest catalytic activity but lowest selectivity among the tested catalysts. Bimetallic catalysts with Cu content equal to the monolayer dispersion capacity displayed a slightly lower activity than that of Pt/TiO2 and 100% selectivity to p-chloroaniline. A lower Cu content led to decreased p-chloroaniline selectivity, while a higher Cu content resulted in markedly inhibited catalytic activity despite of 100% p-chloroaniline selectivity. The findings in the present study indicate that Pt@Cu/TiO2 with a monolayer Cu content is a prominent catalyst with high activity and selectivity.

Influence of graphene surface chemistry on Ir-catalyzed hydrogenation of p-chloronitrobenzene and cinnamaldehyde: Weak molecule-support interactions

Graphene is an ideal model support to investigate the influence of carbon surface chemistry on catalytic reactions. Here a mild hydrothermal method was developed to synthesize graphene-supported iridium nanocatalysts from graphene oxide. By simply varying the hydrothermal conditions, the physicochemical properties of catalysts can be tuned, which can further affect their catalytic performances. Catalysts obtained at higher H2 pressure during hydrothermal process performed higher catalytic activities for hydrogenation of both p-chloronitrobenzene and cinnamaldehyde, benefiting from their higher reduction degrees of iridium nanoparticles. Interestingly, catalysts obtained at lower hydrothermal temperature performed higher activities for p-chloronitrobenzene hydrogenation but lower activities for cinnamaldehyde hydrogenation, due to their distinct surface chemistry of graphene. Through systematic characterizations on 11 catalysts prepared under various conditions, we found that lower hydrothermal temperature endows graphene with larger lateral dimension and more in-plane oxygenated surface groups, which facilitates the accessibility of nitro groups to catalyst surface via H-bond interaction as confirmed by density functional theory calculations. This is not true for cinnamaldehyde, of which adsorption on graphene via π-π stacking interaction is favorable for its hydrogenation.

Preparation of a Pt/Active Carbon Fiber Catalyst and Its Application in the Synthesis of p-Chloroaniline with Catalytic Hydrogenation.

In this study, a Pt loaded active carbon fiber (Pt/ACF) catalyst was prepared by immobilizing Pt nanoparticles on ACF. The catalyst accelerated hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CA) at lower temperature and atmospheric pressure, resulting in approximately 100% yield and selectivity. Several factors that affect p-CA yield were investigated. The nitro reduction rate reached 100% under the optimal reaction conditions, indicating excellent selectivity of the prepared catalyst. This process will overcome the environmental pollution problems associated with the traditional process, and is a green synthetic process.

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.

The promoted catalytic hydrogenation performance of bimetallic Ni-Co-B noncrystalline alloy nanotubes.

A noncrystalline Ni–B alloy in the shape of nanotubes has demonstrated its superior catalytic performance for some hydrogenation reactions. Remarkable synergistic effects have been observed in many reactions when bimetallic catalysts were used; however, bimetallic noncrystalline alloy nanotubes are far less investigated. Here, we report a simple acetone-assisted lamellar liquid crystal approach for synthesizing a series of bimetallic Ni–Co–B nanotubes and investigate their catalytic performances. The dilution effect of acetone on liquid crystals was characterized by small-angle X-ray diffraction (SAXRD) and scanning electron microscopy (SEM). The Ni/Co molar ratio of the catalyst was varied to study the composition, porous structure, electronic interaction, and catalytic efficiency. In the liquid-phase hydrogenation of p-chloronitrobenzene, the as-prepared noncrystalline alloy Ni–Co–B nanotubes exhibited higher catalytic activity and increased stability as compared to Ni–B and Co–B alloy nanotubes due to electronic interactions between the nickel and cobalt. The excellent hydrogenation performance of the Ni–Co–B nanotubes was attributed to their high specific surface area and the characteristic confinement effects, compared with Ni–Co–B nanoparticles.

Stable single-atom platinum catalyst trapped in carbon onion graphitic shells for improved chemoselective hydrogenation of nitroarenes

Supported platinum (Pt) catalysts present excellent chemoselectivity for a variety of hydrogenation reactions. Minimizing the use of such expensive catalysts while retaining their catalytic activities has been one of the most challenging topics in recent years. The construction of well dispersed, stable Pt single atom catalysts both increases the density of catalytically active sites while reducing Pt usage. Here we report the synthesis of Pt single atoms trapped in carbon onion graphitic shells by arc-discharge in aqueous solution. Such graphitic shells not only limit the chemical/thermal coarsening of Pt single atoms, but also enhance the conductivity for accelerating the penetration and exchange of ions and electrons during the catalytic process. Experimental results demonstrate that the Pt single atom catalysts show superior performance and no detectable loss of activity and selectivity over 10 cycles (both remain >99%) for the hydrogenation of p-chloronitrobenzene. This novel atomically dispersed form of Pt catalyst is indicative of a new avenue towards efficient synthesis of single atom catalysts with improved performance.

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.

Selectivity Control on Hydrogenation of Substituted Nitroarenes through End-On Adsorption of Reactants in Zeolite-Encapsulated Platinum Nanoparticles.

Platinum nanoparticles encapsulated into zeolite Y (Pt@Y catalyst) exhibit excellent catalytic selectivity in the hydrogenation of substituted nitroarenes to form the corresponding aromatic amines, even after complete conversion. With the hydrogenation of p-chloronitrobenzene as a model, the role of zeolite encapsulation toward perfect selectivity can be attributed to constraint of the substrate adsorbed on the platinum surface in an end-on conformation. This conformation results in the activation of only one adsorbed group, with little influence on the other one in the molecule. Owing to a much lower apparent activation energy of Pt@Y for the hydrogenation of a separately adsorbed nitro group than that of the adsorbed chloro group, the Pt@Y catalyst can prevent hydrodechlorination of p-chloronitrobenzene under mild conditions. Moreover, such a conformation results in a reduced adsorption energy of target p-chloroaniline on the platinum surface; thus suppressing the reactivity of hydrodechlorination of p-chloroaniline to circumvent further C-Cl bond breakage.

Magnetic Pd nanocatalyst Fe3O4@Pd for C–C bond formation and hydrogenation reactions

Small core-shell Fe3O4@Pd superparamagnetic nanoparticles (MNPs) were obtained with good control in size and shape distribution by metal-complex thermal decomposition in organic media. The role of the stabilizer in the synthesis of MNPs was studied, employing oleylamine (OA), triphenylphosphine (TPP) and triphenylamine (TPA). The results revealed that, among the stabilizer investigated, the presence of oleylamine in the reaction media is crucial in order to obtain an uniform shell of Pd(0) in Fe3O4@Pd MNPs of 7 ± 1 nm. The synthesized core-shell MNPs were tested in Pd-catalyzed Heck-Mizoroki and Suzuki-Miyaura coupling reactions and p-chloronitrobenzene hydrogenation. High conversion, good reaction yields, and good TOF values were achieved in the three reaction systems with this nanocatalyst. The core-shell nanoparticle was easily recovered by a simple magnetic separation using a neodymium commercial magnet, which allowed performing up to four cycles of reuse.

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.

Hydrogenation of p-Chloronitrobenzene on Au Nano-Clusters: Effects of Support.

Gold nanocluster has been reported to have high activity and selectivity for various liquid phase hydrogenation reactions. In this study, gold clusters were loaded on various supports, i.e., TiO2, ZnO, Fe2O3, ZrO2, and CeO2. The Au-cluster catalysts were prepared by deposition-precipitation method using HAuCl4 as the precursor. These catalysts were characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The catalytic properties of these catalysts were studied in a batch slurry reactor for hydrogenation of p-chloronitrobenzene (p-CNB) at 1.1 MPa H2 pressure, 373 K and 300 rpm. The activity decreased in the following order: Au/TiO2 ≧ Au/ZnO ≧ Au/CeO2 (Nikki) ≧ Au/CeO2 (Evonik) ≧ Au/Fe2O3 ≧ Au/ZrO2. TiO2-supported Au clusters had a higher activity than others, due to its hydrophilicity.

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%).