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Title: Targeted synthesis of silicomolybdic acid (keggin acid) inside mesoporous silica hollow spheres for friedel-crafts alkylation
Authors: Dou, J.
Zeng, H.C. 
Issue Date: 3-Oct-2012
Citation: Dou, J., Zeng, H.C. (2012-10-03). Targeted synthesis of silicomolybdic acid (keggin acid) inside mesoporous silica hollow spheres for friedel-crafts alkylation. Journal of the American Chemical Society 134 (39) : 16235-16246. ScholarBank@NUS Repository.
Abstract: Herein we report an inside-out preinstallation-infusion-hydration method for targeted synthesis of Keggin heteropoly acids (silicomolybdic acid, H 4SiMo12O40) within mesoporous silica (SiO 2) hollow spheres. In this process, discrete molybdenum dioxide (MoO2) nanoparticles with diameter size ranging from 25 to 60 nm were first prepared by a one-pot hydrothermal route in water/ethanol mixed solvents at 180 °C, which were then used as cores to grow the shell of supramolecular templated silica with tetraethyl orthosilicate (TEOS) and hexadecyltrimethyl- ammonium chloride (CTACl) in alkaline solution. By thermal treatment of as-synthesized MoO2@SiO2 core-shell spheres, the organic template was burned off and mesoporous shell was formed (BET specific surface area was as high as 872 m2/g). Meanwhile, the encapsulated MoO 2 was oxidized to Mo6+ and infused to the mesoporous silica shells, forming heptamolybdate species (Mo7O24 6-) uniformly dispersed on the mesopore surfaces of silica, while generating void space at the center of spheres. After hydration with water, H4SiMo12O40 was formed by reaction between the surface Mo7O24 6- and silica species in the presence of water. The prepared H4SiMo12O40 @mSiO2 hollow spheres were tested for Friedel-Crafts alkylation of toluene by benzyl alcohol. The H4SiMo12O 40@mSiO2 catalysts fabricated via this novel route exhibited excellent catalytic activity toward benzylation of toluene, which was approximately 2.6 times as high as that of commercial Amberlyst-15 catalyst. In addition, the H4SiMo12O40@mSiO2 catalyst was very robust and could be reused after regeneration. © 2012 American Chemical Society.
Source Title: Journal of the American Chemical Society
ISSN: 00027863
DOI: 10.1021/ja3055723
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