Iron-Modified MCM-48 Mesoporous Molecular Sieves

Abstract

MCM-48 mesoporous molecular sieves containing iron(III) were obtained using a direct sol−gel route followed by removal of the cetyltrimethylammonium hydroxide template before calcination. UV−visible, ESR, and XANES spectroscopies show that iron mostly occupies tetrahedral sites of the siliceous walls. The formation of oxide nanoclusters in the channels is favored in the presence of the organic template molecules during calcination.

Catalytic activity of mesoporous catalysts in Friedel–Crafts benzylation of benzene

“…All samples exhibit a peak around 260 nm. This band is assigned to the charge transfer between the Fe 3+ and O 2-atoms in the framework of Fe-O-Si, indicating isolated, tetrahedrally-coordinated Fe species [19]. In addition to this peak, a shoulder appeared at around 330 nm in the Fe-2 sample which would be consistent with the presence of polyferrate (Fe-O-Fe) n in the framework.…”

Characterization of Iron Atoms in the Framework of MFI-Type Zeolites by UV Resonance Raman Spectroscopy

“…Silicalite-I has no bands in the 200-700 nm region, while Fe-ZSM-5 shows a strong absorption band centered at 240-250 nm. The band at 240-250 nm may be assigned to the dπ-pπ charge-transfer transition between the iron and oxygen atoms in the framework of Fe-O-Si in zeolite (19,20). Similar phenomena have been observed in Ti-O-Si species of TS-1 (10,21,22).…”

Direct synthesis of highly ordered Fe-SBA-15 mesoporous materials under weak acidic conditions

“…Notably, many efforts have been devoted to the incorporation of Al, Ti and V into SBA-15 [11][12][13][14][15][16][17], including the two-steps pH adjusting methods [14,15], the hydrolysis-controlled methods [15,16], and microwave-hydrothermal procedures [17]. However, the incorporation of Fe into the framework of SBA-15 by simple direct hydrothermal methods prepared in acidic media has rarely been reported [18], although Fe-zeolites and Fe-MCM-41 prepared in basic media have been widely investigated [6,[19][20][21][22][23][24][25]. It has been reported that Fe species in the framework of mesoporous materials such as MCM-41 [23], MCM-48 [24], and HMS [25] are tetrahedral coordinated but easily escape from the framework and turn to iron oxide when these materials are calcined at high temperature to remove the organic template.…”

“…However, the incorporation of Fe into the framework of SBA-15 by simple direct hydrothermal methods prepared in acidic media has rarely been reported [18], although Fe-zeolites and Fe-MCM-41 prepared in basic media have been widely investigated [6,[19][20][21][22][23][24][25]. It has been reported that Fe species in the framework of mesoporous materials such as MCM-41 [23], MCM-48 [24], and HMS [25] are tetrahedral coordinated but easily escape from the framework and turn to iron oxide when these materials are calcined at high temperature to remove the organic template. Metal ions are generally in an isolated state in acidic solution, whereas they easily precipitate from solution to form metal oxides in basic solution.…”