Transition metal containing mesoporous silicas - redox properties, structure and catalytic activity

Mesoporous silicas of the MCM-41 type, containing iron, were prepared by synthesis and after framework synthesis, including deposition of iron from dried methanolic solution of iron(III) nitrate. Concentration of iron was up to 12 wt.%. In situ EXAFS, NO adsorption followed by IR spectroscopy and temperature programmed reduction suggest that the resulting iron in most cases is present mainly in the form of isolated iron entities. Depending on the preparation procedures, subtle differences in bonding of iron to the framework were observed. In the oxidation of large hydrocarbons to oxygenates with N2O the most active catalysts are aluminium containing materials. The main difference between FeZSM-5 and FeMCM-41 materials is the presence of Fe-O nanoclusters in FeZSM-5 which seem to be more active in the oxidation reaction than isolated iron entities in mesoporous materials. (C) 2001 Elsevier Science B.V. All rights reserved.