Isomorphous substitution of Fe3− in zeolite LTL

Autor: Ko Yong Sig, Wha-Seung Ahn
Rok vydání: 1997
Předmět:
Zdroj: Microporous Materials. 9:131-140
ISSN: 0927-6513
DOI: 10.1016/s0927-6513(96)00104-6
Popis: Fe-modified L-type zeolites were synthesized hydrothermially, partially substituting iron atoms for the framework aluminum of L-type zeolite. Chemical analysis, XRD, SEM, IR, UV VIS DRS, EPR, XAS, TG DTA, and catalytic activity studies provided the evidence of Fe3 present in the zeolite framework. Both the lattice parameters and the unit cell volume of L-type zeolites containing Fe3 increased with increasing iron content. The change in crystal morphology was obvious from a synthesis mixture in which the molar ratio of Fe2O3Al2O3 is above 0.015. The framework IR bands were shifted to lower frequencies as Fe3 incorporation into the lattice increased, and a new Si-O-Fe bond vibration was located near 668 cm−1. The presence of a signal at g = 4.4 in the EPR spectra was assigned to Fe3 isomorphously substituted in the tetrahedral positions. EXAFS at the Fe K-edge revealed that the Fe3 ions were present in the zeolite framework in a four-fold coordination with an average Fe-O distance of 1.85 A. In the UV VIS spectra, an absorption was observed at 378.7 nm which was assigned to the presence of Fe3 in the zeolite framework. TG DTA studies indicated that Fe-modified L-type zeolite lower thermal stability than the corresponding normal L-type zeolite. A toluene alkylation study reflected the acidity strength of zeolite L being weakened due to the presence of lattice iron species.
Databáze: OpenAIRE
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