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

Abstract

In this paper some Co(II)–Schiff base complexes were immobilized on SiO 2–Al 2O 3 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 SiO 2–Al 2O 3 mixed-oxide have an easily oxidizable environment, which led to higher catalytic activity and selectivity.