Comparison of the redox properties of iron incorporated in different amounts into MCM-41

Mesoporous Fe-MCM-41 samples with different framework iron contents were tested as catalysts in CO oxidation and characterized by TPR, Mossbauer and FTIR spectroscopies after heat treatment in high vacuum and reductive or oxidative atmospheres. In samples with Si/Fe ratios of 20 and 12 all of the iron was found to be reducible with H-2, but only a part of Fe(III) species could be reduced to Fe(II) in materials with lower iron content. In neither of the materials could Fe(III) be fully converted with CO to the divalent oxidation state. A significant part of iron can be reversibly reduced and reoxidized in successive redox cycles. Large Fe-O clusters could not be detected.