Direct synthesis, characterization and catalytic application of SBA-15 mesoporous silica with heteropolyacid incorporated into their framework

The Keggin phosphotungstic acid, H₃PW₁₂O₄₀ (HPW) incorporated into SBA-15 ordered mesoporous silica were synthesized via a method involving the introduction of HPW in an acidified solution of P123 triblock copolymer (EO₂₀PO₇₀EO₂₀), the SBA-15 mesostructuring agent (direct synthesis). Samples with similar HPW loadings were also prepared by impregnation of SBA-15. A comparison between direct incorporation of HPW into mesoporous silica and impregnation of HPW on mesoporous silica was done. Characterization by elemental analysis, XRD, N ₂ adsorption, TEM, DRS-UV and FTIR spectroscopy showed that after calcination HPW in the direct synthesized samples was better dispersed or may even be partially embedded in the pore walls. Moreover, their catalytic behaviors were investigated in the alkylation of o-xylene with styrene. Results show that direct synthesized sample has the better catalytic performances in terms of yield and stability. This behavior may be owing to high dispersion of the HPW species on the SBA-15 and the strong interaction between the HPW and the support, thus prevent HPW leaching from the support.