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- The influence of multiwalled carbon nanotubes and graphene oxide additives on the catalytic activity of 3d metal catalysts towards 1-phenylethanol oxidationPublication . Da Costa Ribeiro, Ana Paula; Fontolana, Emmanuele; Alegria, Elisabete; Kopylovich, Maximilian; Bertani, Roberta; Pombeiro, Armando3d metal (Cu, Fe, Co, V) containing composite catalysts for the solvent-free microwave-assisted trans-formation of 1-phenylethanol to acetophenone with tert-butyl hydroperoxide (TBHP) as oxidant wereprepared by ball milling. The influence of multiwalled carbon nanotubes (CNTs) and graphene oxide (GO)additives on the catalytic activity of the catalysts was studied. CNTs or GO were mixed by ball millingwith the metal salts (CoCl2), oxides (CuO, Fe2O3, V2O5) or binary systems (Fe2O3-CoCl2, CoCl2-V2O5, CuO-Fe2O3). For CoCl2-based catalytic systems, addition of small amounts (0.1–5%) of CNTs or GO leads tosignificant improvement in catalytic activity, e.g. 1% of the CNTs additive allows to rise yields from 28to 77%, under the same catalytic conditions. The CoCl2-5%CNTs composite is the most active among thestudied ones with 85% yield and TON of 43 after 1 h
- Effect of phenolic compounds on the synthesis of gold nanoparticles and its catalytic activity in the reduction of nitro compoundsPublication . Alegria, Elisabete; Da Costa Ribeiro, Ana Paula; Mendes, Marta; Ferraria, Ana Maria; Rego, Ana; Pombeiro, ArmandoGold nanoparticles (AuNPs) were prepared using an eco-friendly approach in a single step by reduction of HAuCl4 with polyphenols from tea extracts, which act as both reducing and capping agents. The obtained AuNPs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet–visible spectroscopy (UV–vis), and X-ray photoelectron spectroscopy (XPS). They act as highly efficient catalysts in the reduction of various aromatic nitro compounds in aqueous solution. The effects of a variety of factors (e.g., reaction time, type and amount of reducing agent, shape, size, or amount of AuNPs) were studied towards the optimization of the processes. The total polyphenol content (TPC) was determined before and after the catalytic reaction and the results are discussed in terms of the tea extract percentage, the size of the AuNPs, and their catalytic activity. The reusability of the AuNP catalyst in the reduction of 4-nitrophenol was also tested. The reactions follow pseudo first-order kinetics.
- Catalytic oxidation of cyclohexane with hydrogen peroxide and a tetracopper(II) complex in an ionic liquidPublication . Da Costa Ribeiro, Ana Paula; Martins, Luisa; HAZRA, SUSANTA; Pombeiro, ArmandoThe catalytic peroxidative oxidation (with H2O2) of cyclohexane in an ionic liquid (IL) using the tetracopper(II) complex [(CuL)2(μ4-O,O′,O′′,O′′′-CDC)]2·2H2O [HL = 2-(2-pyridylmethyleneamino)benzenesulfonic acid, CDC = cyclohexane-1,4-dicarboxylate] as a catalyst is reported. Significant improvements on the catalytic performance, in terms of product yield (up to 36%), TON (up to 529), reaction time, selectivity towards cyclohexanone and easy recycling (negligible loss in activity after three consecutive runs), are observed using 1-butyl-3-methylimidazolium hexafluorophosphate as the chosen IL instead of a molecular organic solvent including the commonly used acetonitrile. The catalytic behaviors in the IL and in different molecular solvents are discussed.
- Highly selective cyclohexane oxidation catalyzed by ferrocene in ionic liquid mediumPublication . Martins, Luisa; Da Costa Ribeiro, Ana Paula; Pombeiro, ArmandoBackground: Although economically very important in view of the significance of the oxidized products for the manufacture of adipic acid and caprolactam (precursors to polyamides widely used in several industries), the current cyclohexane oxidation industrial process leads to very low conversions (ca. 4%) to assure a reasonable selectivity (ca. 85%). Therefore, there is an urgent need to develop sustainable selective cyclohexane oxidation chemistry, which is the main objective of this work. Methods: The partial oxidation of cyclohexane by aqueous tert-butyl hydroperoxide (TBHP, 70% aq. sol.) in phosphonium ionic liquid medium [P6.6.6.14][DCA] and in the presence of catalytic amounts of ferrocene was investigated. The reaction proceeded during 2 h at room temperature. Results: It was found that TBHP, under the above conditions, oxidizeD cyclohexane with high selectivity (> 98%), yielding mainly cyclohexanone (up to 16%, based on the substrate) with total TOFs up to 1 x 104 h-1. Conclusion: The combination of a commercial iron-complex catalyst (ferrocene) and well-adjusted unconventional reaction conditions led to a highly selective, fast and reusable catalytic system for the mild oxidation of cyclohexane. Moreover, the found [Fe(C5H5)2]/[P6.6.6.14][DCA] catalytic system can be of significance to produce polyamide 6.
- ZnO nanoparticles: An efficient catalyst for transesterification reaction of alpha-keto carboxylic estersPublication . Soliman, Mohamed Mostafa Aboelhassan; Karmakar, Anirban; Alegria, Elisabete; Da Costa Ribeiro, Ana Paula; Rubio, Guilherme; Saraiva, Marta S.; Guedes Da Silva, M. Fátima C.; Pombeiro, ArmandoPure ZnO nanoparticles were synthesized by a sustainable precipitation method using zinc nitrate and sodium hydroxide in aqueous medium at room temperature. They were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM-EDX), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-vis) spectroscopy and Brunauer-Emmett-Teller (BET) analysis. The XRD patterns indicate the formation of the hexagonal wurtzite phase with high purity and SEMEDS analysis confirm the purity and a homogenous distribution of the nanostructures. The ZnO nanostructures present plate-like agglomerates, resulting in a quasi-spherical morphology. The catalytic activity of the formed ZnO nanoparticles was evaluated towards the transesterification reaction of different carboxylic esters in the presence of various alcohols. This catalyst is highly selective for the transesterification of alpha-keto carboxylic ester (methyl benzoylformate) and leads to ca. 97% of product yield within 24 h of reaction time.