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.