Mesoporous organosilica containing niobium for environmentally benign oxidation reactions with hydrogen peroxide

Izabela Nowak 

Adam Mickiewicz University, Faculty of Chemistry, Grunwaldzka 6, Poznań 60-780, Poland

Abstract

A synthetic protocol for the preparation of a variety of high-quality periodic mesoporous organosilicas containing niobium (Nb-PMOs) is presented. The nanostructured Nb-PMOs have been synthesized either by the hydrolysis and condensation of bridged silsesquioxane precursors ((EtO)3Si-R-Si(OEt)3,R - ethylene or octylene) or by the co-condensation of tetraethyl orthosilicate and organosilanes. Functionalized materials were prepared by using precursors containing an incremental increase in methylene [(-CH2-)n, n = 2-8)] or vinylene or phenylene groups. Nonionic or cationic templates were employed as the structure directors using the surfactant approach. The evidence for the successful preparation of the Nb-PMOs was based on X-ray diffraction and transmission electron microscopy (high periodicity), nitrogen adsorption (high surface area, monomodal pore size distribution), DRUV-Vis (Nb in framework band) and FTIR spectroscopies (C-Si band). As the Nb-PMOs are expected to find applications as a water-tolerant solid catalyst for those reactions requiring weak acidic sites and low temperatures, they were tested in the oxidation reactions (epoxidation and hydroxylation). The increase in the chain length of precursor was a contributing factor for the increased hydrophobicity and thus a better selectivity. It is interesting to note that all catalysts with the bridged or functionalized framework exhibited higher activity than the pure niobiosilica catalyst, although they had similar structural/textural properties.

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Presentation: Oral at E-MRS Fall Meeting 2006, Symposium B, by Izabela Nowak
See On-line Journal of E-MRS Fall Meeting 2006

Submitted: 2006-06-02 08:04
Revised:   2009-06-07 00:44
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