Oxidation of ethylbenzene using some recyclable cobalt nanocatalysts: The role of linker and electrochemical study

In this paper some Co(II)–Schiff base complexes were immobilized on SiO2–Al2O3 mixed-oxide using two linkers with different flexibilities (3-aminopropyl and 2-aminoethyl-3-aminopropyl). The synthesized materials were characterized by FT-IR spectroscopy, UV–Vis, CHN elemental analysis, ICP-MS, EPR, SEM, TEM, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The catalytic activity of the heterogenized Co(II)–Schiff base complexes in the oxidation of ethylbenzene was studied without the need of any solvent, at 353 K, using tert-butyl hydroperoxide as oxygen source. The best catalyst has a higher catalytic activity (86%) and selectivity to acetophenone (99%) at TBHP/ethylbenzene molar ratio (1:1), and could be reused at least 4 times without significant loss in acetophenone yield, suggesting that no complex leaching took place under the reaction conditions. The electrochemical data about oxidation of the immobilized Co(II)–Schiff base complexes at the surface of multi-walled carbon nanotubes was also studied. The results indicate that the Co-complexes anchored on the modified SiO2–Al2O3 mixed-oxide have an easily oxidizable environment, which led to higher catalytic activity and selectivity.

Co(II)–Schiff base complexes covalently linked on the organo-functionalized SiO2–Al2O3 mixed-oxides. The catalytic activities of the heterogenized cobalt nanocatalysts in the oxidation of ethylbenzene were studied without the need of any solvent. In addition, the electrochemical data about oxidation of cobalt nanocatalysts at the surface of multi-walled carbon nanotubes was also studied.Figure optionsDownload high-quality image (141 K)Download as PowerPoint slideResearch highlights
► The cobalt complexes supported on functionalized SiO2–Al2O3 used as nanocatalysts.
► Nanocatalysts were studied in the oxidation of ethylbenzene to acetophenone.
► Without the need of any solvent.
► The selectivity of acetophenone reached to 99% at TBHP/ethylbenzene molar ratio (1:1).
► Electrochemical behavior of the Co nanoparticles was studied.