The state of iron sites in the calcined FeAlPO4-5 and its tuning to the property of microporous AlPO4-5 molecular sieve

• Iron state diversity of calcinated Fe incorporated FeAlPO4-5.
• Direct observation of single Fe site distribution by Cs-corrected STEM.
• Enhanced acidity, π bond adsorption and HDS performance as tuning to AlPO4-5.

The dispersion and coordination is critical to the nature of metal phases. This article describes an approach of single Fe sites preparing under microporous environment via calcination of the Fe incorporated FeAlPO4-5 as well as the tuning to the property of AlPO4-5 molecular sieve. The UV, Raman, EPR spectroscopies and H2-TPR characterization revealed through the extraction of framework Fe inside the micropore by calcination, extra-framework Fe sites were generated, the dispersion of which was higher than Fe sites of impregnated Fe2O3/AlPO4-5, and it indicated that part of Fe sites of FeAlPO4-5 can be with coordination vacancy. It is notable that the presence of single Fe sites was directly observed by Cs-corrected STEM micrograph. NH3-TPD and toluene-TPD results both exhibited an enhanced acidity and π bond adsorption ability of FeAlPO4-5 toward AlPO4-5 and the impregnated sample Fe2O3/AlPO4-5. Finally, the FeAlPO4-5 turned out to perform higher thiophene desulfurization rate against AlPO4-5 and impregnated sample, which can be related to the improvement in the adsorption ability and reactivity for the single Fe sites inside the microporous environment.

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