The use of mesoporous molecular sieves containing niobium for the synthesis of vegetable oil-based products

A synthetic protocol for the preparation of periodic mesoporous organosilicas containing niobium (Nb-PMOs) is presented. The nanostructured bridged organoniobosilicates have been synthesized by the acid catalyzed hydrolysis and condensation of bridged silsesquioxane precursors containing two different organic bridging groups ((C2H5O)(3)Si-R-Si(OC2H5)(3), R: ethylene or octylene) in the presence of nonionic template P123. The retention of niobium and organic groups in the organosilica framework was ensured by slow template removal. A successful synthesis of Nb-PMOs was confirmed by powder X-ray diffraction (high periodicity), N-2 adsorption (surface area about 900 m(2) g(-1) and narrow pore size distribution with maximum at about 4-11 nm), transmission electron microscopy (hexagonal symmetry), diffuse reflectance UV-visible spectroscopy (characteristic absorption band for Nb in the framework), H-2-temperature-programmed reduction (localization of Nb in the framework) and FTIR spectroscopy (presence of CH2-Si(OSi )(3) groups). Experiments show that increasing the content of the organic chain length functionality in the precursors is found to significantly worsen the mesostructural ordering of the product. It is shown that the niobium can act as a co-template in making nanoporous organosilica materials. The presence of niobium species neighboring with organic bridges in Nb-PMOs offers new prospects for application of these materials in catalysis. These niobosilicate materials showed excellent catalytic activity and selectivity for direct oxidation of vegetable oil ingredients into valuable products under mild liquid phase conditions using dilute H2O2 as an oxidant. (C) 2008 Elsevier B.V. All rights reserved.