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- Ball milling as an effective method to prepare magnetically recoverable heterometallic catalysts for alcohol oxidationPublication . Fontolan, Emmanuele; Alegria, Elisabete; Da Costa Ribeiro, Ana Paula; Kopylovich, Maximilian; Bertani, Roberta; Pombeiro, ArmandoHeterometallic double Fe2O3–CoCl2, CoCl2–V2O5, MoO3–V2O5, and triple CuO–Fe2O3–CoCl2 3d metal dispersed systems were easily prepared by ball milling at room temperature and characterized by scanning electron microscopy (SEM), field emission gun scanning electron microscopy (FEGSEM), energydispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). They catalyze the microwave-assisted solvent-free heterogeneous oxidation of 1-phenylethanol to acetophenone with tert-butyl hydroperoxide (t-BuOOH) as oxidant, used as a model reaction. In most of the heterometallic systems a significant improvement in the catalytic activity was observed in comparison to homometallic ones. For the tested catalytic systems and experimental conditions, the CuO–Fe2O3–CoCl2 and Fe2O3–CoCl2 systems exhibit the highest activity with maximum 78% yield and TON 39 after 1 h. The possibility of magnetic recovery of the catalysts was demonstrated for the Fe2O3–CoCl2 (3:1) system.
- New trendy magnetic C-scorpionate iron catalyst and its performance towards cyclohexane oxidationPublication . Da Costa Ribeiro, Ana Paula; Matias, Inês; Alegria, Elisabete; Ferraria, Ana Maria; Rego, Ana; Pombeiro, Armando; Martins, LuisaFor the first time, a magnetic C-scorpionate catalyst was prepared from the iron(II) complex [FeCl2{_3-HC(pz)3}] (pz = pyrazol-1-yl) and ferrite, using the sustainable mechanochemical synthetic procedure. Its catalytic activity for the cyclohexane oxidation with tert-butyl hydroperoxide (TBHP) was evaluated in different conditions, namely under microwave irradiation and under the effect of an external magnetic field. The use of such magnetic conditions significantly shifted the catalyst alcohol/ketone selectivity, thus revealing a promising, easy new protocol for tuning selectivity in important catalytic processes.
- Mechanochemical preparation of Pd(II) and Pt(II) composites with carbonaceous materials and their application in the Suzuki-Miyaura reaction at several energy inputsPublication . Soliman, Mohamed Mostafa Aboelhassan; Peixoto, Andreia F.; Da Costa Ribeiro, Ana Paula; Kopylovich, Maximilian; Alegria, Elisabete; Pombeiro, ArmandoPd(II) and Pt(II) composites with activated carbon (AC), graphene oxide, and multiwalled carbon nanotubes were prepared by ball milling and used as catalysts for the Suzuki-Miyaura reaction, under several energy inputs (mechanical grinding, conventional heating, and microwave irradiation). The catalytic composites were characterized by ICP-MS, BET, XPS analyses, TEM, and SEM. The average particle size of the prepared composites was estimated to be in the range of 6-30 nm, while the loadings of Pd and Pt did not significantly affect the surface area of the AC support due to the tendency to agglomerate as observed by the TEM analysis. The Pd/AC composites exhibit high mechanochemical catalytic activity in cross-coupling of bromobenzene and phenylboronic acid with molar yields up to 80% with TON and TOF of 222 and 444 h(-1), respectively, achieved with Pd(4.7 wt%)-AC catalyst under the liquid assisted grinding for 0.5 h at ambient conditions, using cyclohexene as an additive.
- Mechanochemical preparation of Pd and Pt composites for Suzuki-Miyaura reactionsPublication . Soliman, Mohamed M. A.; Da Costa Ribeiro, Ana Paula; Saraiva, Marta S.; Alegria, Elisabete; Pombeiro, ArmandoThe application of green, simple, time- and energy-saving mechanochemical ball-milling procedures for the dispersion of palladium and platinum salts or oxides over MWCNTs (multi-walled carbon nanotubes) and activated carbon is reported. Carbon nanotubes have exceptional properties (e.g. high mechanical strength and surface areas) which make them promising materials for various applications. In this respect, we apply dispersed palladium and platinum composites [1-2] as catalysts in the Suzuki-Miyaura reactions. Both the preparation of the dispersed materials and the catalytic Suzuki-Miyaura reactions were performed by ball-milling and the results are discussed.
- Simple solvent-free preparation of dispersed composites and their application as catalysts in oxidation and hydrocarboxylation of cyclohexanePublication . Alegria, Elisabete; Fontolan, Emmanuele; Da Costa Ribeiro, Ana Paula; Kopylovich, Maximilian; Domingos, Catarina; Ferraria, Ana Maria; Bertani, Roberta; Botelho do Rego, Ana M.; Pombeiro, ArmandoA simple and clean mechanochemical synthesis at room temperature was employed to prepare CuO-Fe2O3-CoCl2 (100 nm scale), MoO3-V2O5, CuO-CoCl2, Fe2O3-CoCl2, CuO-V2O5, Cu(CH3COO)(2)-V2O5, Cu(CH3COO)(2)-MoO3 (1-100 mm scale) 3d metal based dispersed composites with different ratios of components using simple metal salts/oxides and multiwalled carbon nanotubes (CNT) or graphene oxide (GO) additives (CoCl2-CNT, CoCl2-GO). The thus prepared composite materials were characterized by Xray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), field emission gun scanning electron microscopy (FEGSEM), energy-dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). XPS analysis revealed no metal redox change upon ball milling treatment, which however promotes metal hydroxylation. The catalytic activity of the prepared composites in the heterogeneous low power microwave-assisted oxidation of cyclohexane with aq. H2O2 at 30 degrees C was notorious with yields up to 31% and selectivity up to 94% towards cyclohexanol (upon treatment with PPh3) for the CuO-CoCl2-based material. The hydro-carboxylation of cyclohexane with CO, water and K2S2O8 to produce cyclohexanecarboxylic acid bearing one more carbon atom at 60 degrees C is achieved with yields up to 17% for the reaction performed in the presence of the CuO-CoCl2 catalyst. The clean CuO-CoCl2 (1:2) catalyst preparation and the catalytic reaction (oxidation of cyclohexane) can be achieved in one-pot at low temperature, without any added organic solvent, and by using exclusively the mechanochemical energy input, with a marked 23% yield at 30 degrees C.
- Comparison of microwave and mechanochemical energy inputs in the catalytic oxidation of cyclohexanePublication . Da Costa Ribeiro, Ana Paula; Alegria, Elisabete; Kopylovich, Maximilian; Ferraria, Ana Maria; Rego, Ana; Pombeiro, ArmandoThe effect of microwave and mechanochemical ball milling energy inputs was studied for the peroxidative oxidation (with aqueous H2O2) of cyclohexane to cyclohexanol and cyclohexanone, over CoCl2 and/or V2O5 dispersed (μm scale) catalysts. A maximum total yield of cyclohexanol and cyclohexanone of 43% after 1 h of reaction at 30 °C, in acetonitrile and under microwave irradiation (5 W), was achieved over the CoCl2–V2O5 (3 : 1) catalyst prepared by ball milling. Cyclohexanol is the main final product with a selectivity of up to 93% over cyclohexanone. Conducting the oxidation reaction under microwave irradiation under the same conditions but without any mechanochemical treatment of the catalyst prior to use resulted in a lower total yield of 30% with a lower selectivity (69%) towards cyclohexanol over cyclohexanone. The sole application of mechanochemical treatment for the catalyst preparation and the catalytic oxidation of cyclohexane allowed to reach yields of 29% after 1 h of reaction, at room temperature, without microwave irradiation and any additive and in the absence of any organic solvent. Ball milling is shown to provide a convenient, solvent-free method to disperse these solid catalysts and to promote the above cyclohexane oxidation, although, in the latter case, not so effectively as microwave irradiation.