Liquid-phase hydrodechlorination of chlorinated benzenes over active carbon supported nickel catalysts under mild conditions

Liquid phase hydrodechlorination of chlorinated benzenes was studied over Ni/active carbon (Ni/AC), Ni/gamma-Al2O3, Ni/SiO2 and Raney Ni. The complete dechlorination of chlorobenzene (ClBz) was realized at 333-343 K on Ni/AC under hydrogen atmosphere of 1.0 MPa in the presence of alkaline hydroxide. Dichloro- and trichlorobenzenes were also hydrodechlorinated with 50-95% yields of benzene under the similar conditions, as above. The reaction follows zero-order to ClBz concentration and 1.9 order to hydrogen pressure. The reaction does not proceed in the absence of alkaline hydroxide, suggesting the complete coverage of active nickel surface with produced chlorine and the removal of the chlorine ion with hydroxide ion as a rate-limiting step. The active catalysts were characterized by H-2 chemisorption and transmission electron microscopy techniques. The apparent activity strongly depends on the active area of nickel on catalyst surface. (C) 2004 Published by Elsevier B.V.

Multi-walled carbon nanotubes supported Pt-Fe cathodic catalyst for direct methanol fuel cell

Multi-walled carbon nanotubes supported Pt-Fe cathodic catalyst shows higher specific activity towards oxygen reduction reaction as compared to Pt/MWNTs when employed as cathodic catalyst in direct methanol fuel cell.

Performance of palladium-containing supported catalysts in the oxidation of 1-butene

Performance of palladium-containing supported catalysts in the oxidation of 1-butene was investigated in a fixed-bed flow microreactor. The Pd-Fe-HCl/Ti-Al catalyst is the best among the five Pd-Fe-HCl/X (A = SiO2, gamma-Al2O3, Al-Ti, TiO2, MCM-22) catalysts for the oxidation of I-butene to butanone. It is interesting that high propionic acid selectivity can be obtained when V and H2SO4 are added to the palladium-containing supported catalysts.

Ammonia synthesis on graphitic-nanofilament supported Ru catalysts

Graphitic-nanofilaments (GNFs) supported ruthenium catalysts were prepared and characterized by NZ physisorption, X-ray diffraction (XRD), transmission electron microscope (TEM) and temperature programmed reduction-mass spectroscopy (TPR-MS) and used for ammonia synthesis in a fixed bed microreactor. The TEMs of the Ru/GNFs and Ru-Ba/GNFs catalysts indicate that the Ru particles are in the range of 2-4 nm, which is the optimum size of Ru particles for the maximum number of B5 type sites. The activity of Ru-Ba/GNFs catalysts is higher than that of Ru-Ba/AC by about 25%. The methanation reaction on the Ru/GNFs catalyst is remarkably inhibited compared with a Ru/AC catalyst. High graphitization of GNFs is likely to be the reason for the high resistance to the methanation reaction. The power rate law for ammonia synthesis on Ru-Ba/GNFs catalysts can be expressed by r = Kp(NH3)(-0.4) P-N2(0.8) P-H2(-0.7), indicating that H-2 is an inhibitor for N-2 activation on the catalyst. Catalysts with the promoters Ba, K and Cs show large differences in activity for ammonia synthesis. The catalyst promoted with Ba (Ba/Ru = 0.2 molar ratio) was found to be the most active, whereas that with a K promoter was the least active. (C) 2003 Elsevier B.V. All rights reserved.

Promoting effects in hydrogenation and hydrodesulfurization reactions on the zirconia and titania supported catalysts

Tetralin hydrogenation (HYD) and thiophene hydrodesulfurization (HDS) were studied for the supported MoS2 and WS2 sulfides, either non-promoted or promoted with Co and Ni. The supports used were ZrO2, alumina-stabilized TiO2 and pure alumina. Preparation of catalysts included presulfidation of non-promoted system with subsequent addition of promoter and resulfidation. It has been found that the nature of promoter plays determining role for the catalytic performance. The most active in both HYD and HDS reactions are Ni-promoted Mo and W catalysts, supported on ZrO2. (C) 2003 Published by Elsevier B.V.

Catalytic decomposition of hydrazine over supported molybdenum nitride catalysts in a monopropellant thruster

The catalytic decomposition of hydrazine over a series of MoNx/gamma-Al2O3 catalysts with different Mo loadings was investigated in a monopropellant thruster (10 N). When the Mo loading is equal to or higher than the monolayer coverage of MoO3 on gamma-Al2O3, the catalytic performance of the supported molybdenum nitride catalyst is close to that of the conventionally used Ir/gamma-Al2O3 catalyst. The MoNx/gamma-Al2O3 catalyst with a loading of about 23wt% Mo (1.5 monolayers) shows the highest activity for hydrazine decomposition. There is an activation process for the MoNx/gamma-Al2O3 catalysts at the early stage of hydrazine decomposition, which is probably due to the reduction of the oxide layer formed in the passivation procedure.

Polymerization of ethylene to branched polyethylene with silica and Merrifield resin supported nickel(II) catalysts with alpha-diimine ligands

Silica and Merrifield resin were used as carriers for the support of alpha-diimine nickel(II) precatalysts for ethylene polymerization. The alpha-diimine ligands containing allyl were modified by introducing the reactive Si-Cl end-group, allowing their immobilization via a direct reaction of the Si-Cl groups with the silanols on silica surface or the hydroxyls on the ethanolamine-modified Merrifield resin. The resulting supported alpha-diimine ligands were characterized by analytical and spectroscopic techniques (NMR and Fr-IR).

Hydrogenation of phenol in scCO(2) over carbon nanofiber supported Rh catalyst

A catalyst of Rh nanoparticles supported on a carbon nanofiber, 5 wt.% Rh/CNF, with an average size of 2-3 nm has been prepared by a method of incipient wetness impregnation. The catalyst presented a high activity in the ring hydrogenation of phenol in a medium of supercritical CO2 (scCO(2)) at a low temperature of 323 K. The presence of compressed CO2 retards hydrogenation of cyclohexanone to cyclohexanol under the reaction conditions used, and this is beneficial for the formation of cyclohexanone, increasing the selectivity to cyclohexanone.

Rare earth metal alkyl complexes bearing N,O,P multidentate ligands: Synthesis, characterization and catalysis on the ring-opening polymerization of L-lactide

Alkane elimination reactions of rare earth metal tris(alkyl)s, Ln(CH2SiMe3)3(THF)2 (Ln = Y, Lu) with the multidentate ligands HL1-4, afforded a series of new rare earth metal complexes. Yttrium, complex I supported by flexible amino-intino phenoxide ligand HL1 was isolated as homoleptic product. In the reaction of rigid phosphino-imino phenoxide ligand HL 2 with equintolar Ln(CH2SiMe3)3(THF)2, HL 2 was deprotonated by the metal alkyl and its imino C=N group was reduced to C-N by intramolecular alkylation, generating THF-solvated mono-alkyl complexes (2a: Ln = Y; 2b: Ln = Lu). The di-ligand chelated yttriurn complex 3 without alkyl moiety was isolated when the molar ratio of HL 2 to Y(CH,SiMe3)3(THF)2 increased to 2: 1. Reaction of steric phosphino beta-ketoiminato ligand HL 3 with equimolar Ln(CH2SiMe3)3(THF)2 afforded di-ligated mono-alkyl complexes (4a: Ln = Y; 4b: Ln = Lu) without occurrence of intramolecular alkylation or formation of homoleptic product. Treatment of tetradentate methoxy-amino phenol HL 4 with Y(CH2SiMe3)3(THF)2 afforded a monomeric yttrium bis-alkyl complex of THF-free. The resultant complexes were characterized by IR, NMR spectrum and X-ray diffraction analyses.All alkyl complexes exhibited high activity toward the ring-opening polymerization Of L-lactide to give isotactic polylactide with controllable molecular weight and narrow to moderate polydispersity.

Developments and applications of supported liquid phase catalysts

Supported liquid phase catalyst (SLPC) is one of effectively heterogenized homogeneous catalysts using organometallic complexes as active components, which are dissolved in a small quantity of liquid phase dispersed in the form of isle or film on the surface of supports. The SLPC has successfully been applied for several chemical transformations and this article will review recent results with respect to the preparation and catalytic performance, the applicability to continuous flow operations, and the capability of multifunctional catalysis.

Surface-appropriate lipophobicity - Application in isobutene oligomerization over Teflon-modified silica-supported 12-silicotungstic acid

A series of silica-supported 12-silicotungstic acid catalysts (H4SiW12O40, abbreviated as HSiW), modified with various loadings of Teflon (HSiW/SiO2-Teflon), were prepared by an impregnation method. The surface properties of the catalysts were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), BET, infrared (IR) spectroscopy, NH3-TPD and the Drop Shape Analysis (DSA). SEM results combined with energy-dispersive X-ray (EDX) measurements of HSiW/SiO2-Teflon revealed that F-compound (Teflon) is effectively coated on the catalyst surface. The contact angles for water and oil of 50 wt% HSiW/SiO2 and HSiW/SiO2-Teflon indicate that HSiW/SiO2-Teflon catalyst enhances not only the surface hydrophobicity but also the surface lipophobicity by means of the addition of Teflon. Silica-supported 12-silicotungstic acid modified with Teflon exhibits higher C-8(=) selectivity and longer lifetime than that of silica-supported 12-silicotungstic acid in isobutene oligomerization. Thus, surface-appropriate lipophobicity of catalysts may be effective for decreasing the interaction between coke precursors and the catalyst surface and for removing deposited coke more easily.

Isobutane/butene alkylation over supported heteropoly acid catalysts: I. Influence of the structure of silica

Catalysts consisting of heteropoly acids (HPAs) supported on different silica and mesoporous molecular sieves have been prepared by impregnation and the sol-gel method, respectively, and their catalytic behavior in fixed-bed alkylation of isobutane with butene has been investigated. The activity, selectivity and stability of the supported-HPA catalysts could be correlated with the surface acidity of the catalysts, the structure of supports as well as the time on stream (TOS). In the fixed-bed reactor, the acidity of the heteropoly acid is favorable to the formation of dimerization products (C-8(=)); especially, the pore size of supports was seen to have an important effect on activity and product distribution of the catalysts. Contrary to the traditional solid-acid catalysts, the supported-HPA catalysts own an excellent stability for alkylation, which makes it possible for these supported catalysts to replace the liquid-acid catalysts used in industry.