Influence of CTA-MCM-41 Synthesis Basicity on the Catalytic Transesterification Stability

Hybrid silicas synthesized with cationic surfactants have basic sites due to the presence of siloxy anions (equivalent to SiO-) generated by charge balance with the surfactant polar head (usually CTA(+)). Several modifications can be used in their synthesis to increase the catalytic activity of these silicas. One way is by replacing the CTA(+) cation with others with different hydrophilic heads to improve site basicity and control particle shape and size to increase site accessibility. However, despite having excellent catalytic activity in transesterification, they usually deactivate during reuse. In this work, hybrid silicas were synthesized, varying the molar ratio of CTABr: SiO2 and the basicity of the synthesis mixture to verify the influence of these parameters on the number of siloxy sites and catalytic stability. The hybrid silicas were characterized by X-ray diffraction, thermogravimetry, scanning electron microscopy and catalytically evaluated in the model transesterification reaction between methanol and ethyl acetate. The results showed that the increase in pH of the synthesis caused a rise in the number of cations retained in the structure and a more significant amount of siloxy sites. This effect provided the formation of more catalytically stable hybrid silicas after reuse in transesterification.