Au/TiO₂@SBA-15 nanocomposites as catalysts for direct propylene epoxidation with O₂ and H₂ mixtures

A nanostructured Au/TiO₂@SBA-15 catalyst has been prepared and applied in propylene epoxidation with a mixture of O₂/H₂. The mesopores of SBA-15 were first deactivated by grafting of hydrophobic groups. Titanium was then selectively grafted in the micropores of SBA-15 by reaction with titanium isopropoxide followed by calcination and deposition of Au nanoparticles. The nanocomposite catalysts exhibited relatively stable propylene oxide (PO) production with small amounts of propanal and acetone byproducts. A catalyst prepared by grafting with trimethylsilyl groups, a Ti/Si ratio of 0.05 and very small Au nanoparticles (<2 nm), showed the highest catalytic activity. The improved performance appears to be related to the interaction of very small Au nanoparticles in close contact with very small sized TiO₂ domains in combination with the hydrophobicity of the fully open mesopores. The results demonstrate the possibility to improve the catalytic performance of Au-Ti catalysts through rational catalyst design.