Coordination and Oxidation States of Iron Incorporated in Mesoporous MCM41

摘要

Mesoporous Fe―MCM41 samples (Si/Fe = 25) were synthesized and characterized under evacuation and reducing/oxidizing treatments by in situ FTIR and Mossbauer spectroscopies. Both Fe(Ⅱ) and Fe(Ⅲ) located in low coordination states in top layers of pore walls exhibit Lewis acidity and may participate in Fe(Ⅲ) reversible Fe(Ⅱ) processes at low temperatures (570 K). Furthermore, Fe(Ⅲ) reversible Fe(Ⅱ) cycles can be achieved and repeated with participation of the full amount of iron at higher temperatures (670 K). The accompanying formation of oxygen vacancies and restoration of the structure in the reverse process does not result in extended damages; the MCM41 structure retains its stability under the conditions applied.