Microwave-assisted catalysis by iron oxide nanoparticles on MCM-41: Effect of the support morphology

Catalytically active heterogeneous catalysts have been prepared via microwave deposition of iron oxide nanoparticles (0.5–1.2 wt%) on MCM-41 type silica materials with different morphologies (particles, helical and spheres). This methodology leads to iron oxide nanoparticles composed by a mixture of FeO and Fe2O3 species, being the Fe(II)/Fe(III) peak ratio near to 1.11 by XPS. DRUV spectroscopy indicates the presence of tetrahedral coordinated Fe3+ in the silica framework of the three catalysts as well as some extraframework iron species in the catalysts with particle and sphere-like morphologies. The loading of the nanoparticles does neither affect the mesopore arrangement nor the textural properties of the silica supports, as indicated by SAXS and nitrogen adsorption/desorption isotherms. A detailed investigation of the morphology of the supports in various microwave-assisted catalyzed processes shows that helical mesostructures provide optimum catalytic activities and improved reusabilities in the microwave-assisted redox (selective oxidation of benzyl alcohol) catalyzed process probably due to a combination of lower particle size and higher acidity in comparison with the supports with particle and sphere morphology.

J.G.M. and R.L. gratefully acknowledge funding under project CTQ2011-28954-C02-01(02) (MICINN) from the Spanish MICINN. R.L. is also grateful for financial support via the concession of a RyC contract (RYC 2009 04199) and funding under the project P10-FQM-6711 (Consejeria de Ciencia e Innovacion, Junta de Andalucia). E.S. is grateful for financial support under the JdC program (ref. JCI 2008–2165) and from GV (ref. BEST2011/223).