Loading...
4 results
Search Results
Now showing 1 - 4 of 4
- Ultrasound and radiation-induced catalytic oxidation of 1-phenylethanol to acetophenone with iron-containing particulate catalystsPublication . Soliman, Mohamed Mostafa Aboelhassan; Kopylovich, Maximilian N.; Alegria, Elisabete; Da Costa Ribeiro, Ana Paula; Ferraria, Ana Maria; Rego, Ana; Correia, Luís M. M.; Saraiva, Marta S.; Pombeiro, ArmandoIron-containingparticulatecatalystsof0.1–1 µmsizewerepreparedbywetandball-milling procedures from common salts and characterized by FTIR, TGA, UV-Vis, PXRD, FEG-SEM, and XPS analyses. It was found that when the wet method was used, semi-spherical magnetic nanoparticles were formed, whereas the mechanochemical method resulted in the formation of nonmagnetic microscale needles and rectangles. Catalytic activity of the prepared materials in the oxidation of 1-phenylethanol to acetophenone was assessed under conventional heating, microwave (MW) irradiation, ultrasound (US), and oscillating magnetic field of high frequency (induction heating). In general, the catalysts obtained by wet methods exhibit lower activities, whereas the materials prepared by ball milling afford better acetophenone yields (up to 83%). A significant increase in yield (up to 4 times) was observed under the induction heating if compared to conventional heating. The study demonstrated that MW, US irradiations, and induction heating may have great potential as alternative ways to activate the catalytic system for alcohol oxidation. The possibility of the synthesized material to be magnetically recoverable has been also verified.
- Synergistic catalytic action of vanadia-titania composites towards the microwave-assisted benzoin oxidationPublication . Ferretti, Francesco; Da Costa Ribeiro, Ana Paula; Alegria, Elisabete; Ferraria, Ana Maria; Kopylovich, Maximilian; Guedes Da Silva, M. Fátima C.; Marchetti, Fabio; Pombeiro, ArmandoIntensification of chemical processes according to the motto "faster, simpler, greener" is among the main concerns nowadays. One of the ways of intensification is the application of synergistic catalytic effects when the overall efficiency of a composite catalyst is much higher than the sum of the component activities. Here, we report on the preparation of synergistic catalytic materials by a simple and straightforward ball milling procedure. Oxidation of benzoin was selected as a model reaction to demonstrate the viability of the concept. For the V2O5-TiO2 (95 : 5) composite material, the synergistic effect is triggered by low power microwave irradiation with more than a tenfold jump in the catalytic activity in comparison to the activities of the individual components.
- 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.