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. (C) 2011 Elsevier B.V. All rights reserved.