Recyclable Ni(II), Cu(II), and Co(II) complexes containing Schiff base immobilized on nanosilica as catalysts in oxidation of hydrocarbons

Metal complexes (M=Ni, Cu, and Co) containing Schiff base have been synthesized and characterized using the usual coordination chemistry techniques. The complexes were immobilized in silica nanoparticle functionalized with a Schiff base (SB) and the heterogeneous catalysts were characterized by infrared spectroscopy, Scanning electron microscopy (SEM) and determination of the surface area (BET). Thermogravimetric analysis (TGA) of metal concentration was conducted using atomic absorption spectroscopy. The catalysts were studied in the oxidation reaction of hydrocarbons at 50 °C using H₂O₂ or tert-butyl hydroperoxide (TBHP) as oxidant. The heterogeneous catalysts NPs-SiO₂-SB-Co(II) (catalyst 1), NPs-SiO₂-SB-Cu(II) (catalyst 2), and NPs-SiO₂-SB-Ni(II) (catalyst 3) showed moderate activities in the oxidation of cyclohexane, toluene, and benzene using H₂O₂ as oxidant. The results indicated that catalyst 2 displayed better activity in the oxidation of cyclohexane, toluene, and benzene. The best activity was obtained at 50 °C with the following conversions: 88 %, 78 %, and 66 % for cyclohexane, toluene and benzene, respectively. The results of the recycling experiment revealed that the copper complex immobilized in mesoporous silica nanoparticle maintains its catalytic activity after 4 cycle.