Magnetic properties and catalytic performance of iron-containing mesoporous molecular sieves

Fe-containing mesoporous molecular sieves were synthesized by the wet impregnation method with two different metallic loadings. The resulting iron oxide/silica composites were then submitted to a reduction treatment for 6h at 873K, under H-2 flow. The microstructure of both, the Si-MCM-41 host and the impregnated composites were characterized by XRD, N-2 adsorption, DRUV-vis and Mossbauer spectroscopy. The magnetic behavior of each microstructure was characterized by the magnetization dependence on the magnetic field (up to 1.5T) and temperature (between 5 and 300 K). The catalytic performance was tested for cyclohexene oxidation by hydrogen peroxide and further correlated with the observed magnetic properties. It was found that the reduction treatment largely affects the selectivity to reaction products, leading to catalysts exhibiting a selectivity of 80% towards the allylic oxidation products. This is attributed to a large free radical generation arising from the interaction between the hydrogen peroxide and the partially reduced iron species (mainly Fe-0 and Fe3O4), exhibiting superparamagnetic and/or ferromagnetic character. (C) 2010 Elsevier B.V. All rights reserved.