Synthesis and characterization of tungsten-incorporated mesoporous molecular sieve MCM-48 by one step

Abstract

Tungsten-substituted mesoporous MCM-48 materials are successfully synthesized at 393 K by a onestep co-condensation sol-gel method. The prepared samples with different Si/W ratios are characterized by X-ray diffraction (XRD), nitrogen adsorption, high-resolution transmission electron microscopy (HRTEM), diffuse reflectance UV-visible spectroscopy and FT-IR, and the results indicate the presence and good dispersion of tungsten species inside the silica pores, the Si/W ratio is controlled above 28. When the Si/W ratio is less than 28, though no bulk tungsten is detected outside the MCM-48 mesoporous silica, the pore structure order becomes worse.

Tungsten doped mesoporous SBA‐16 as novel heterogeneous catalysts for oxidation of cyclopentene to glutaric acid

“…DR UV‐Vis spectra of the W‐SBA‐16 catalysts are shown in Figure . The W‐SBA‐16 catalysts show two absorption bands at ~230 and ~265 nm; those two bands can be ascribed to a ligand‐to‐metal charge transfer in the isolated [WO 4 ] tetrahedral species and a charge transfer from O 2‐ to W 6+ , which indicates the existence of a partially octahedrally coordinated tungsten oxide species in SBA‐16 . A band at ~380 nm for bulk WO 3 is observed in the W‐SBA‐16(5, 10, and 20) catalysts, and the absence of this band in the W‐SBA‐16(30, 40, and 50) catalysts is consistent with the results in Figure .…”

Enhancing tungsten oxide/SBA-15 catalysts for hydrolysis of cellobiose through doping ZrO2

“…W 30 Zr 0 /SBA-15 exhibited a strong absorption band at ∼389 nm, accompanied by relatively weak bands at 218 and 273 nm (trace a). These bands are related to crystalline WO 3 [46,47], isolated WO 4 tetrahedral species [40,48,49], and partially polymerized W species in octahedral coordination [40,47], respectively. Since the absence of ZrO 2 in this sample, the presence of the band at 218 nm suggests that besides the large crystalline WO 3 on the external surface, a fraction of isolated W atoms are well dispersed in the framework of SBA-15.…”

A Comparative Characterization of the HPA‐MCM‐48 Type Catalysts Produced by the Direct Hydrothermal and Room Temperature Synthesis Methods

“…The aging/crystallization period was followed by the washing stage. In literature, in most of the studies [4][5][6][7][8][9], no detailed information is given concerning the washing stage of the MCM-48 synthesis. However, it is known that any excess surfactant or other basic material accompanying the MCM-48 precursor will be removed through a careful washing procedure increasing the calcination efficiency [23], pore volume, and BET surface area.…”

“…Hence a low heating rate (1 • C/min) was employed and a long total calcination time of 15 hours was achieved. The calcination temperature was chosen as 823 K since it was commonly employed in literature [5][6][7]9] and was shown to be the optimum calcination temperature for MCM-41 type materials [25] which have very similar properties with MCM-48 type materials except for the pore geometries.…”

“…MCM-48 type materials with cubic pore geometries were first synthesized by the Mobil researchers in the year 1992 as a member of the new family of mesoporous materials named as the M41S family [1,2]. Owing to high BET surface areas (up to 1600 m 2 /g), high pore volumes (up to 1.2 cm 3 /g), and narrow pore size distributions in the mesoporous region [3][4][5], they have been the subject of many different studies ever since [4][5][6][7][8][9][10].…”