Liquid-phase Hydrogenation Of P-chloronitrobenzene Research Articles

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.

A Novel Synthesis of Gold Nanoparticles Supported on Hybrid Polymer/Metal Oxide as Catalysts for p-Chloronitrobenzene Hydrogenation

This contribution reports a novel preparation of gold nanoparticles on polymer/metal oxide hybrid materials (Au/P[VBTACl]-M metal: Al, Ti or Zr) and their use as heterogeneous catalysts in liquid phase hydrogenation of p-chloronitrobenzene. The support was prepared by in situ radical polymerization/sol gel process of (4-vinyl-benzyl)trimethylammonium chloride and 3-(trimethoxysilyl)propyl methacrylate in conjunction with metal-alkoxides as metal oxide precursors. The supported catalyst was prepared by an ion exchange process using chloroauric acid (HAuCl4) as gold precursor. The support provided the appropriate environment to induce the spontaneous reduction and deposition of gold nanoparticles. The hybrid material was characterized. TEM and DRUV-vis results indicated that the gold forms spherical metallic nanoparticles and that their mean diameter increases in the sequence, Au/P[VBTACl]-Zr > Au/P[VBTACl]-Al > Au/P[VBTACl]-Ti. The reactivity of the Au catalysts toward the p-CNB hydrogenation reaction is attributed to the different particle size distributions of gold nanoparticles in the hybrid supports. The kinetic pseudo-first-order constant values for the catalysts in the hydrogenation reaction increases in the order, Au/P[VBTACl]-Al > Au/P[VBTACl]-Zr > Au/P[VBTACl]-Ti. The selectivity for all the catalytic systems was greater than 99% toward the chloroaniline target product. Finally the catalyst supported on the hybrid with Al as metal oxide could be reused at least four times without loss in activity or selectivity for the hydrogenation of p-CNB in ethanol as solvent.

Pd0.01Ru0.01Ce0.98O2−δ: A highly active and selective catalyst for the liquid phase hydrogenation of p-chloronitrobenzene under ambient conditions

Nanostructured bimetal ion substituted ceria, Pd0.01Ru0.01Ce0.98O2−δ (PdRuC2), prepared for the first time by a novel solution combustion synthesis and characterized employing XRD, BET, HRTEM and XPS has been shown to be very active and selective than the monometal ion substituted analogue Pd0.02Ce0.98O2−δ (PdC2), whereas Ru0.02Ce0.98O2−δ (RuC2) is inactive towards liquid phase hydrogenation of p-chloronitrobenzene to p-chloroaniline under ambient conditions. Structural studies show metal ion substituted ceria as the predominant phase. The hydrogenation over PdRuC2 is completed beyond 75min with 100% selectivity. Conversely, PdC2 hydrogenates ~40% of p-chloronitrobenzene with 82% selectivity. Increase of temperature from 35°C to 80°C showed a little higher activity of PdRuC2 but with a lower selectivity. The as-prepared and aged forms of PdRuC2 showed similar activity, whereas PdRuC2 heat-treated at 500°C increased the conversion and the 800°C heated catalyst reduced it (both ~2%) indicating high thermal stability. Maximum hydrogenation activity has been observed in ethanol as compared to methanol and butanol. The PdRuC2 catalyst also shows excellent hydrogenation activity towards o-, m-chloronitrobenzene and nitrobenzene. The enhancement of activity and selectivity of Pd in presence of Ru in the PdRu bimetal ionic catalyst for the hydrogenation reaction has been attributed to involvement of remarkable Ru4+-promotion in Pd0.01Ru0.01Ce0.98O2−δ.

Au/Mo2N as a new catalyst formulation for the hydrogenation of p-chloronitrobenzene in both liquid and gas phases

The batch liquid phase hydrogenation of p-chloronitrobenzene over MO2N resulted in the sole formation of p-chloroaniline. Incorporation of Au nanoparticles (mean size = 8 nm) enhanced hydrogen uptake with a fourfold increase in rate, retention of ultraselectivity with stability over repeated reaction cycles. Reaction exclusivity to p-chloroaniline extended to continuous gas phase operation where Au/MO2N outperformed Au/Al2O3 as a benchmark. Under the same conditions, Pd/MO2N was non-selective, generating nitrobenzene and aniline via combined hydrodechlorination and hydrogenation. These results demonstrate the viability of Au/MO2N as a new catalyst formulation in selective substituted nitroarene hydrogenation. (C) 2012 Elsevier B.V. All rights reserved.

The effect of poly- N-vinylpyrrolidone modification on NiCoB catalysts for hydrogenation of p-chloronitrobenzene

A series of poly- N-vinylpyrrolidone (PVP)-modified NiCoB catalysts with various PVP contents were prepared by chemical reduction method. The Ni and Co cations were reduced by NaBH 4 at room temperature. PVP was added during preparation. The materials were characterized by X-ray diffraction, transmission electron microscopy, and differential scanning calorimeter. The results showed that all samples possessed amorphous structure. After washing, the residual PVP adsorbed on the surface of NiCoB and acted as a spacer to prevent NiCoB particles from aggregation and agglomeration. The liquid-phase hydrogenation of p-chloronitrobenzene was carried out to investigate the catalytic properties of the PVP-modified NiCoB catalysts. The catalytic activities of NiCoB catalysts decreased by modifying with PVP but the selectivities for p-chloroaniline improved significantly. The competitive adsorption of PVP with p-chloronitrobenzene and p-chloroaniline on the NiCoB nanoparticles was responsible for the catalytic performance. The amount of the PVP played a key role in the hydrogenation reaction.

Ni-B amorphous alloy deposited on an aminopropyl and methyl co-functionalized SBA-15 as a highly active catalyst for chloronitrobenzene hydrogenation

The synthesis and characterization of SBA-15 type mesoporous silica containing surfaces functionalized with aminopropyl and methyl groups (NH 2&CH 3-SBA-15) were reported. The Ni-B amorphous alloy deposited on such support showed higher activity and selectivity in liquid-phase hydrogenation of p-chloronitrobenzene ( p-CNB) to p-chloroaniline ( p-CAN) owing to the synergetic promotions from both the aminopropyl and methyl groups. The aminopropyl could greatly enhance the dispersion of Ni-B alloy particles via coordination with Ni 2+ ions, leading to high activity. While, the methyl could enhance the surface hydrophobicity which facilitated the desorption of the target product p-CAN and thus inhibited its further dechlorination. Besides, the strong hydrophobicity also enhanced the B-content in the Ni-B alloys, which favored the activation and hydrogenation of the NO 2-group in p-CNB molecule, leading to high selectivity. This work clearly reveals the importance of organization of different functional groups on the surface of heterogeneous catalysts.

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.

Hydrogenation of p-chloronitrobenzene on Ni–B Nanometal Catalysts

A series of Ni–B catalysts were prepared by mixing nickel acetate in 50% ethanol/water or methanol/water solution. The solution of sodium borohydride (1 M) in excess amount to nickel was then added dropwise into the mixture to ensure full reduction of nickel cations. The mol ratio of boron to nickel in mother solution was 3 to 1. The effects of preparation conditions such as temperature, stirring speed, and sheltering gas on the particle size, surface compositions, electronic states of surface atoms and catalytic activities of the Ni–B catalysts were studied. Ranel nickel catalyst was included for comparison. These catalysts were characterized by N2 sorption, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The catalysts were tested for liquid phase hydrogenation of p-chloronitrobenzene. All of the catalysts prepared in this study had nanosized particles. The preparation condition has significant influence on the particle size and surface compositions of the catalyst. The Ni–B catalyst was passivated by boron; therefore it was more stable than Raney nickel and did not catch fire after exposure to air. The catalysts prepared under N2 flow could suppress the oxidation of Ni by the dissolved oxygen in water and had metallic state of nickel. The catalyst prepared with vigorous stirring at 25°C under N2 stream yielded the smallest particles and resulted in the highest activity. It was much more active than the Raney nickel catalyst. The reaction condition also has pronounced effect on the hydrogenation activity. Using methanol as the reaction solvent increased p-chloronitrobenzene conversion to a large extent, compared to that using ethanol as the reaction medium. The selectivity of main product (p-chloroaniline) was greater than 99% on all of the Ni–B catalysts.

Liquid-Phase Selective Hydrogenation of p-Chloronitrobenzene on Ni−P−B Nanocatalysts

A series of Ni−P−B catalysts were prepared by liquid-phase reduction. Nickel acetate and sodium hypophosphite were mixed in ethanolic solution. The solution of sodium borohydride in excess amount was then added dropwise into the aforementioned mixture to ensure full reduction of the Ni cations. The Ni:P:B ratios in the mother solution was fixed at 1:3:3. These catalysts were characterized by powder X-ray diffraction, nitrogen sorption, transmission electron microscopy, and X-ray photoelectron spectroscopy. The effects of preparation conditions such as temperature, stirring speed, and sheltering gas on the particle size, surface compositions, oxidation states of surface atoms, and catalytic activities of the Ni−P−B catalysts were studied. The catalysts were tested by liquid-phase hydrogenation of p-chloronitrobenzene at 393 K and 1.2 MPa hydrogen pressure in a batch reactor. Raney nickel catalyst was included for comparison. The preparation condition had significant influence on the particle size and surfa...

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.

Hydrogenation of aromatic nitro compounds on copper-modified platinum catalysts

The gas and liquid phase hydrogenations of nitrobenzene and liquid phase hydrogenation of p-chloronitrobenzene on Pt-Cu catalysts were studied. The effect of the copper content on a catalyst was examined, and a relationship was sought between the degree of occupation of the platinum surface by copper and the decrease in the hydrogenation activity in the liquid phase hydrogenation of nitrobenzene. The mechanism of this reaction is discussed.