Catalytic transesterification by hybrid silicas containing CnTA+ surfactants

The MCM-41 silica possesses a structure characterized by a hexagonal mesoporous organization with a uni-dimensional system of pores. This as-synthesized silica contains cations (usually C(16)TA(+)) in the pores and catalytic sites that are basic due to the presence of the siloxy ions ( SiO-) associated with the cations. This work investigates the effects of the use of cationic alkyltrimethylammonium bromide surfactants (C(n)TABr, where n = 10, 12, 14, or 16) on the catalytic properties of silicas containing these occluded cations. The hybrid silicas were synthesized at a temperature of 30 degrees C, using a synthesis time of 2 h, and were subsequently characterized by X-ray diffractometry, thermogravimetry, and scanning electron microscopy. The basicity of the siloxy sites modified by the cations used in the synthesis of the hybrid silicas was evaluated using X-ray photoelectron spectroscopy. The results obtained using a model monoester transesterification catalytic reaction showed that the TOF0 value increased with the size of the hydrophobic tail of the surfactant and was highest for the catalyst prepared with C(16)TABr. In addition, the hybrid silicas presented increased relative intensity (RI%) and smaller particle size.