Catalytic activity of anionic iron(III) porphyrins immobilized on grafted disordered silica obtained from acidic leached chrysotile

Hydrated disordered silica obtained by leaching chrysotile with hydrochloric acid was grafted with 3-APTS and reacted with aqueous iron porphyrins solutions of [Fe(TDFSPP) and Fe(TCFSPP)]. The obtained materials were characterized by powder X-ray diffraction (PXRD), Uv-vis, FTIR and electron paramagnetic resonance (EPR) spectroscopies and investigated as catalysts in oxidation reaction of cyclohexane using iodosylbenzene as oxidant. The catalytic activities obtained in heterogeneous media for Fe(TDFSPP) was superior to the results obtained in homogeneous conditions but the opposite effect was observed for the Fe(TCFSPP), indicating that instead of the structural similarity of both iron porphyrins (second generation porphyrins), the immobilization way produced different catalysts. The best catalytic activity of the Fe(TDFSPP)/Si-3-APTS (65%) compared to Fe(TCFSPP)/Si-3-APTS (33%) can be explained by the easy access of the oxidant and the substrate to the catalytic sites in the former. A schematic representation for the immobilization and a mechanism for the oxidation reaction have been presented. (c) 2005 Elsevier B. V. All rights reserved.