Papers by A.P.C. Ribeiro
The use of gold as a promotor of alkane hydrocarboxylation is reported for the first time. Cycloh... more The use of gold as a promotor of alkane hydrocarboxylation is reported for the first time. Cyclohexane hydrocarboxylation to cyclohexanecarboxylic acid (up to 55% yield) with CO, water, and peroxodisulfate in a water/acetonitrile medium at circa 50 °C has been achieved in the presence of gold nanoparticles deposited by a colloidal method on a carbon xerogel in its original form (CX), after oxidation with HNO3 (-ox), or after oxidation with HNO3 and subsequent treatment with NaOH (-ox-Na). Au/CX-ox-Na behaves as re-usable catalyst maintaining its initial activity and selectivity for at least seven consecutive cycles. Green metric values of atom economy or carbon efficiency also attest to the improvement brought by this novel catalytic system to the hydrocarboxylation of cyclohexane.
Publications by A.P.C. Ribeiro
The highly efficient eco-friendly synthesis of ketones (yields over 99%) from secondary alcohols ... more The highly efficient eco-friendly synthesis of ketones (yields over 99%) from secondary alcohols is achieved by combination of [FeCl2{η3-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.
C-Scorpionate vanadium(IV) [VO x Cl 3Àx {k 3-RC(pz) 3 }] [pz = pyrazol-1-yl; x = 0, R = SO 3 (1);... more C-Scorpionate vanadium(IV) [VO x Cl 3Àx {k 3-RC(pz) 3 }] [pz = pyrazol-1-yl; x = 0, R = SO 3 (1); x = 1, R = CH 2 OH (2)o r CH 2 OSO 2 Me (3)] complexes supported on functionalized carbon nanotubes (CNTs) are the first V-scorpionate catalysts used so far for the neat oxidation of o-, m-o rp-xylene, with TBHP (70 %a queous solution), to the corresponding toluic acids (main products), tolualdehydes and methylbenzyl alcohols. Remarkably,ap-toluic acid yield of 43 %(73 %s electivi-ty,T ON = 1.34 10 3)w as obtained with 2@CNT in as imple microwave-assisted mild oxidation procedure, using av ery low catalyst charge(3.2 10 À2 mol % vs. substrate). Further, this occurred in the absence of any bromine source, what is significant towards the development of ag reener and more sustainable process for oxidation of xylenes. Moreover,r euse of catalysts with preservation of their activity was found for up to six consecutive cycles. Thee ffects of reaction parameters , such as reaction time, temperature, amount of catalyst or type of heating source,o nt he performance of the above catalytic systems are reported and discussed.
A B S T R A C T Gold nanoparticles were deposited on different carbon materials and used as catal... more A B S T R A C T Gold nanoparticles were deposited on different carbon materials and used as catalysts for the alkane hydro-carboxylation reaction. Cyclohexane hydrocarboxylation to cyclohexanecarboxylic acid was carried out in the presence of CO and water, peroxodisulfate, in water/acetonitrile medium, at ca. 50 °C, with gold nanoparticles deposited by a colloidal method on carbon nanotubes and activated carbon with three different surface che-mistries: in their original forms (CNT or AC, respectively), oxidized with HNO 3 (ox) or oxidized with HNO 3 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).
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Papers by A.P.C. Ribeiro
Publications by A.P.C. Ribeiro