EXAFS STUDY OF Fe/ZSM-5 PREPARED BY CHEMICAL VAPOUR DEPOSITION AND Co/FER, MOR, MFI PREPARED BY ION EXCHANGE

摘要

EXAFS spectroscopy is a very powerful tool to gain an insight of the structures of transition-metal complexes embedded in the pores of zeolitic materials. The existence of binuclear oxo-iron clusters in Fe/ZSM-5, which was postulated on the basis of FTIR and CO/H_2 TPR experiments, was unambiguously confirmed by EXAFS. By comparison with data of Fe model-complexes available in the literature, it is proposed that the Fe species adopt a structure closely resembling the "diamond core" of the methane monooxygenase enzyme (Fe(μ-OH)_2Fe). The EXAFS measurements provided Co-O distances and coordination numbers for Co/FER, MFI and MOR samples and thus enabled to characterize the average Co ion site in the zeolite framework. The results also indicated, in agreement with FTIR spectra, that Co ions deform the zeolite support to reach an optimal bonding with the framework.