Browsing by Author "Figueiredo, J. L."
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- Gold nanoparticles deposited on surface modified carbon materials as reusable catalysts for hydrocarboxylation of cyclohexanePublication . Ribeiro, A. P. C.; Martins, Luisa; Carabineiro, S. A. C.; Figueiredo, J. L.Gold nanoparticles were deposited on different carbon materials and used as catalysts for the alkane hydrocarboxylation reaction. Cyclohexane hydrocarboxylation to cyclohexanecarboxylic acid was carried out in the presence of CO and water, peroxodisulfate, in water/acetonitrile medium, at ca. 50 degrees C, with gold nanoparticles deposited by a colloidal method on carbon nanotubes and activated carbon with three different surface chemistries: in their original forms (CNT or AC, respectively), oxidized with HNO3 (ox) or oxidized with HNO3 and subsequently treated with NaOH (-ox-Na). Au/CNT-ox-Na was the best catalyst, yielding cyclohexanecarboxylic acid up to 88.2% yield, with excellent recyclability (97.5% of the initial activity was maintained after five consecutive catalytic cycles).
- Heterogenisation of a c-scorpionate feII complex on carbon materials for cyclohexane oxidation with hydrogen peroxidePublication . Martins, Luisa; Almeida, M. Peixoto de; Carabineiro, S. A. C.; Figueiredo, J. L.; Pombeiro, ArmandoThe hydrotris(pyrazol-1-yl)methane iron(II) complex [FeCl2{h3-HC(pz)3}] (pz=pyrazol-1-yl) (1) was immobilized on three diferente carbon materials (activated carbon, carbon xerogel and multi-walled carbon nanotubes) with three different surface treatments (original, treated with nitric acid, and treated with nitric acid followed by sodium hydroxide) to produce active, selective and recyclable catalysts. The heterogenisation process was more efficient for carbon nanotubes treated with nitric acid and sodium hydroxide. An outstanding improved catalytic performance of complex 1 upon heterogenisation on carbon nanotubes treated with nitric acid and sodium hydroxide (turnover numbers up to 5.6_103 and overall yield of 21 %), relative to the homogeneous system, was achieved for the single-pot peroxidative oxidation of cyclohexane to the cyclohexanone and cyclohexanol mixture. The heterogenised systems allowed their easy recovery and reuse, at least for five consecutive cycles, maintaining 96% of the initial activity and concomitante rather high selectivity to cyclohexanol and cyclohexanone.
- Highly efficient and reusable CNT supported iron(II) catalyst for microwave assisted alcohol oxidationPublication . Martins, Luisa; Ribeiro, A. P. C.; Carabineiro, S. A. C.; Figueiredo, J. L.; Pombeiro, ArmandoThe highly efficient eco-friendly synthesis of ketones (yields over 99%) from secondary alcohols is achieved by combination of [FeCl2{eta(3)-HC(pz)(3)}] (pz = pyrazol-1-yl) supported on functionalized multi-walled carbon nanotubes and microwave irradiation, in a solvent-free medium. The carbon homoscorpionate iron(II) complex is the first one of this class to be used as catalyst for the oxidation of alcohols.
- Homogeneous and heterogenised new gold C-scorpionate complexes as catalysts for cyclohexane oxidationPublication . Almeida, M. Peixoto de; Martins, Luisa; Carabineiro, S. A. C.; Lauterbach, T.; Rominger, F.; Hashmi, A. S. K.; Pombeiro, Armando; Figueiredo, J. L.Gold(III) complexes of type [AuCl2{eta(2)-RC(R'pz)(3)}]Cl [R = R' = H (1), R = CH2OH, R' = H (2) and R = H, R' = 3,5-Me-2(3), pz = pyrazol-1-yl] were supported on carbon materials (activated carbon, carbon xerogel and carbon nanotubes) and used for the oxidation of cyclohexane to cyclohexanol and cyclohexanone, with aqueous H2O2, under mild conditions.