Effect of silica coating on the catalytic activity of maghemite nanoparticles impregnated into mesoporous silica matrix

Abstract

The search for more efficient catalysts and less polluting and less costly reagents has made heterogeneous catalysis one of the most advantageous processes in this scenario. In this work, recoverable heterogeneous catalysts were prepared by incorporating maghemite nanoparticles (M-NP) into mesoporous silica matrix and further coated with dense or mesoporous layers by the sol-gel process. The catalytic activity of the nanocomposites was evaluated in hydrocarbon oxidation accomplished by the epoxidation of Z-cyclooctene. The materials were characterized by small-angle-x-ray scattering (SAXS), transmission electron microscopy (TEM), nitrogen adsorption-desorption analysis that confirms the coating over the nanocomposites and also the dependence of the reagent amount on the thickness of coating. SAXS curves and nitrogen adsorption-desorption analysis are in agreement with typical profiles of well-ordered hexagonal lattice with the surface area obtained from BET analysis of 454 m 2 /g and the pore volume of 0.917 cm 3 /g for the non-coated mesoporous silica. TEM and XRD results show the formation of maghemite phase with nanoparticle diameters between 3.5 and 20 nm. In addition, the catalytic results show that the nanocomposites coated with a mesoporous silica coating displayed higher substrate conversion than those coated with dense silica coating.