Nature of the active sites in CO oxidation on FeSiBEA zeolites

• Nature of iron incorporated in FeSiBEA was identified by DR UV–vis and Mössbauer.
• Two kinds of pseudo-tetrahedral Fe(III) sites were distinguished in FeSiBEA.
• Distorted pseudo-tetrahedral Fe(II) sites exhibited high activity in CO oxidation.
• Model of active iron centre for CO oxidation over FeSiBEA was proposed.

FeSiBEA zeolites containing 1 wt% of iron were prepared by a two-step postsynthesis method in acidic (pH = 2.6) (Fe1.0SiBEA(w)) and alkaline (pH = 10) (Fe1.0SiBEA(p)) conditions. The structure of the studied materials, their acidity as well as the nature and environment of iron present in the samples were studied by means of XRD, FTIR with CO as probe molecule, DR UV–vis, Mössbauer and XPS spectroscopies, respectively. Temperature-Programmed Surface Reaction (TPSR) was used to test the catalytic activity of FeSiBEA zeolites in CO oxidation in air in the temperature range of 298–773 K. It was shown that Fe1.0SiBEA(w) contains iron as framework pseudo-tetrahedral Fe(III), in contrast to Fe1.0SiBEA(p), in which additional octahedral FeOx oligomers were identified. Moreover, the presence of two kinds of pseudo-tetrahedral Fe(III) sites with different distortion was distinguished in Fe1.0SiBEA(w). The higher catalytic activity was showed by Fe1.0SiBEA(w) zeolite containing iron as a strongly distorted pseudo-tetrahedral Fe(III) well dispersed in the framework of SiBEA zeolite. The model of probable active iron centre in Fe1.0SiBEA(w) was presented.

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