Influence of synthesis routes on the state of Fe-species in SBA-15 mesoporous materials

Four different iron-containing SBA-15 based mesoporous materials have been prepared. The first three (DS-1, DS-2 and DS-3) are synthesised directly from the same synthesis gel containing iron - just modifying the second ageing step at different pH values (< 1, 3.5, and 7 respectively). The fourth substance (PS sample) is a grafted material, with iron impregnated after the synthesis. The materials contain iron in different extents and states: with ionic dispersion in DS-1, whereas large hematite crystals are embedded into DS-2 and DS-3 samples. The post-synthesis modification of PS results in deposition of iron oxide particles of 3 - 6 nm most probably within the pore channels. Samples have been characterized among other methods by XRD, TEM and Mossbauer spectroscopy. Although the materials have profoundly different structures, all of them exhibit good activity in the catalytic oxidation of phenol with hydrogen peroxide in aqueous media. In particular, those samples which have embedded hematite particles display even remarkable hydrothermal stability in this process.