title: Effect of aluminum on the nature of the iron species in Fe-SBA-15.
abstract: We report the preparation of highly ordered mesoporous Fe-Al-SBA-15 with isolated extraframework Fe species under acidic conditions. The materials were characterized by means of UV resonance Raman spectroscopy, in conjunction with BET, XRD, TEM, UV-vis, H2-TPR, FT-IR, and 27Al MAS NMR spectroscopy. The addition of both Fe and Al to the synthesis gel of SBA-15 results in the formation of isolated extraframework Fe species located close to the framework Al ions and the Fe content an order of magnitude higher than that in Fe-SBA-15 synthesized without Al. The existence of anchored extraframework Fe species was confirmed by the presence of a strong absorption band at 270 nm, hydrogen reduction at relatively low temperature, and the presence of a resonance Raman band at 1140 cm(-1). The location of Fe in close proximity to framework Al nuclei is further supported by 27Al MAS NMR measurements. Two characteristic UV Raman bands at 510 cm(-1) and 1090 cm(-1) excited by 244-nm laser are assigned to Fe-O-Si symmetric and asymmetric stretching modes of isolated tetrahedral Fe ions in the silica framework for Fe-SBA-15. The resonance Raman band at 1140 cm(-1) excited by 325-nm laser is attributed to the asymmetric stretching mode of the isolated extraframework iron species in Fe-Al-SBA-15. The isolated Fe species close to framework Al species are stable in acidic HCl solution, whereas the majority of Fe species in Fe-SBA-15 can be easily removed.
authors.affiliation: State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Li
authors.forename: Zhaochi
authors.initials: Z
authors.lastname: Feng
authors.forename: Hongchuan
authors.initials: H
authors.lastname: Xin
authors.forename: Fengtao
authors.initials: F
authors.lastname: Fan
authors.forename: Jing
authors.initials: J
authors.lastname: Zhang
authors.forename: Pieter C M M
authors.initials: PC
authors.lastname: Magusin
authors.forename: Emiel J M
authors.initials: EJ
authors.lastname: Hensen
authors.forename: Rutger A
authors.initials: RA
authors.lastname: van Santen
authors.forename: Qihua
authors.initials: Q
authors.lastname: Yang
authors.forename: Can
authors.initials: C
authors.lastname: Li