Synthesis and Characterization of Microporous Fe−Si−O Materials with Tailored Iron Content from Silsesquioxane Precursors

Calcination of mixtures of (c-C5H9)7Si7O9(OH)3, 1, and (c-C5H9)7Si7O12Fe(tmeda), 2 (tmeda = N,N,N‘,N‘-tetramethylethylenediamine), led to microporous amorphous Fe−Si−O materials with adjustable iron content in the range 1−11 wt %. A set of different complementary techniques including N2 physisorption, XRD, XPS, DRUV−vis, RS, IR, HRTEM, and Mössbauer spectroscopy was used to follow the variation of the textural properties, metal dispersion, and speciation with the iron content along the whole mixing series. The calcination of these mixtures produced Fe−Si−O materials having basically the same properties as those observed for the individually calcined iron silsesquioxane. The N2 physisorption indicates high surface areas, rather large pore volumes, and a very narrow pore size distribution with an average pore size diameter around 6−7 Å. The TEM and the spectroscopic analysis of the Fe−Si−O materials indicate that the iron is present mainly as small iron oxide particles highly dispersed throughout silica and to a minor extent as clustered and isolated species. The particle size distribution was estimated to be about 2−8 nm for 11% Fe−Si−O and 2−4 nm for samples with lower iron content. These materials showed catalytic activity in NH3 oxidation and N2O decomposition.