Iron-containing zeotype materials

A large number of papers have reported the synthesis of framework iron-containing zeotype materials. The syntheses of Fe-MFI (82,155), Fe-beta (84), Fe-MTT (156), Fe-MOR (157), Fe-TNU-9/-10 (158), Fe-MCM-41 (159), and Fe-SBA-15 (160) have been described, and the properties of these materials have been characterized. 

Iron can be introduced into the frameworks of zeotype materials during their hydrothermal syntheses. Iron isomorphously substitutes for some silicon atoms in the framework if this route is chosen. The Si, Al, and Fe contents depend on the composition of the synthesis gel. The nature and distribution of the iron species in a particular sample strongly depend on the activation treatments that are appHed after the synthesis. 

There are several papers dedicated to the characterization of iron-containing zeotype materials, with an emphasis on determining the locations of the iron. For example, in an investigation of Fe-MFI, Milanesio et al. (161) used synchrotron X-ray powder difiraction in an attempt to determine the location of the Fe(III) in the MFI lattice. The data provided a rather 

There have also been a few reports of the incorporation of iron into mesoporous materials. Huang et al. discussed the synthesis of Fe-SBA-15, whereby the iron was incorporated by incipient wetness impregnation following the hydrothermal synthesis of the SB A-15 (164). Jiang et al. synthesized Fe-MCM-41 using both direct hydrothermal and postsynthesis methods and claimed that tetrahedral Fe species are present in the MCM-41 firamework (159) and Zhao et al. reported on the synthesis of Fe-MCM-48 using a mixed surfactant method (165). 

There is stiU a dispute as to whether the catalytic activity of iron-containing zeotype materials, for example, Fe-ZSM-5, should be attributed to isomorphously substituted framework iron or to extra-framework iron oxide or iron hydroxide species that are highly dispersed in the material. These extra-framework iron species are present for two reasons, either because they were not incorporated into the framework during the synthesis or because they were ejected from the framework during postsynthesis treatments (such as calcination or other heat treatments). The unresolved issue of the origin of catalytic activity continues to be the subject of research, whereby state-of-the-art characterization techniques are being applied. 

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Aromatization of hydrocarbons Iron-containing zeotype materials... 

Iron incorporation into MFI resulted in the development of another important application for framework metal-containing zeotype materials that is, the abihty to synthesize phenol directly frombenzene using N2O as oxidant. 

Zeotype materials containing metal cations, for example ions of titanium, vanadium, chromium, iron, or tin, in the tetrahedral positions of their frameworks have been explored as solid Lewis acid catalysts (Ig). Such materials have been shown to be active in the Meerwein—Pormdorfr-Verley reduction of carbonyl compounds (151,233), and the BV oxidation (also called BV rearrangement) (234). 

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