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Fabrication, Characterization and Catalytic Hydrogenation Properties of Novel Metal/carbon Composites

Author: XingLi
Tutor: QiuJieShan
School: Dalian University of Technology
Course: Chemical processes
Keywords: Co/C Ni/C solvothermal carbonization co-precipitation method Chloronitrobenzene Selective hydrogenation
CLC: O643.36
Type: PhD thesis
Year: 2007
Downloads: 687
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Abstract


Metal/carbon nanocomposites have drawn much attention due to their promising applications in catalysis, adsorption/separation, electrode materials, hydrogen storage, and antibacterial materials. Metal/carbon composites made by one-pot method for synthesis of metal/carbon precursor usually have high surface areas and controllable pore structure. Metal particles can homogenously disperse in carbon matrix even at high metal loading. These properites make this kind of materials have potential applications in catalysis field. Carbon supported metal catalysts exhibit good CAN selectivity for CNB catalytic hydrogenation. For CNB hydrogenation reactions, highly active precious metal catalysts such as platinum, ruthenium and palladium have been studied extensively. Iron-group metals such as cobalt and nickel show excellent catalytic hydrogenation performance. However, little work has been done about the CNB hydrogenation over the cheap iron-group metals. In this dissertation, Co/C and Ni/C nanocomposites have been successfully synthesized by hydrothermal/solvothermal carbonization co-precipitation process using furfural and cobalt/nickel acetate salts as starting materials. Their catalytic hydrogenation properties are investigated by using CNB hydrogenation as probe reaction.Cobalt and nickel catalysts have been prepared by liquid 1,2-propanediol reduction. The possibility of Co and Ni catalysts used for CNB hydrogenation is discussed preliminarily. The effects of NaOH concentration, reduction time and reduction technique on the morphology, composition and o-CNB hydrogenation catalytic properties of the catalysts have been studied. The results show that sheet-like and spherical nanocobalt with a mixed structure of fcc and hcp can be obtained by using reflux and solvothermal method respectively. Ni spherical nanoparticles with fcc structure are obtained under solvothermal conditions. The selectivity to o-CAN and the conversion of o-CNB could also reach above 99% over the cobalt catalyst made by reflux method at 120℃, 3 MPa. The catalytic activity of the Co catalyst made by solvothermal method (89% o-CNB conversion) is inferior to that of the Co catalyst made by reflux method. However, the selectivity to o-CAN is high (98%). The selectivity to o-CAN is below 90% over Ni catalyst with high o-CNB conversion.Highly dispersed Co/C and Ni/C catalysts have been desiged to synthesize in order to improve the catalytic performance of cobalt and nickel catalysts. Co/C and Ni/C catalysts with high BET surface areas and mesoporous structure have been controllably synthesized with furfural and cobalt/nickel acetate as starting materials by facile simultaneous carbonization co-precipitation process under hydrothermal or solvothermal conditions. The effects of the solvent on the morphologies, compositions, and BET surface areas have been investigated. The results show that the precursors of Co/C and Ni/C catalysts obtained in the mixed H2O-EG solvent (v/v=l) are flower-like microspheres constructed with nanosheets. The morphologies of the precursors can be kept during high temperature carbonization process. The growth mechanisms of the sheet-like precursors of the Co/C and Ni/C catalysts are proposed based on the experimental results.Effect of calcination temperature on o-CNB catalytic hydrogenation properties over the Co/C catalysts made in the mixed H2O-EG solvent (v/v=1) is investigated. The Co/C catalyst made at 700℃shows the highest catalytic activities for the o-CNB hydrogenation, with 98% o-CNB conversion and 97% selectivity to o-CAN at 2 MPa and 140℃. For comparision, Co/AC catalyst with the same cobalt-loading amount has been made by conventional wet-impregnation method using a commercial activated carbon as support. The Co/C catalyst has higher active cobalt surface area and dispersion, and therefore shows more excellent catalytic performance for o-CNB hydrogenation. The catalytic performance of the Ni/C catalyst is evaluated using aromatic nitro compounds hydrogenation as probe reaction. The Ni/C catalyst shows excellent catalytic performance with 97-100% substrate conversions) and 98-100% selectivities to the desired products. The dechlorination for CNB hydrogenation over the catalyst is below 2%. Furthermore, the catalyst can be reused without obviously loss in catalytic activity even after six cycles.Cobalt- or nickel-based catalysts can be easily separated and recovered magnetically after the hydrogenation reaction due to their intrinsic magnetic properties. This provides a convenient way to recover the catalysts from the reaction system.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Chemical kinetics,catalysis > Catalytic > Catalyst
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