Selective oxidation of benzyl alcohol using in situ generated H2O2 over hierarchical Au–Pd titanium silicalite catalysts†

Benzyl alcohol was oxidized by an ‘‘in situ generated’’ hydrogen peroxy species, formed from a dilute mixture of hydrogen and oxygen, under mild conditions at a high rate over gold, palladium and gold–palladium nanoparticles supported on hierarchical titanium silicate materials. Hierarchical TS-1 supports were obtained from the crystallization of silanized protozeolitic units, being characterized by having a secondary porous system within supermicro/mesopore range and an enhanced surface area over a standard reference TS-1 material. The presence of the secondary porosity not only improves the accessibility to the active sites of the relatively large reactant molecules but also enhances the metal dispersion, leading to an improved catalytic performance for alcohol oxidation. The catalytic activity of metal loaded hierarchical TS-1 materials was found to be higher in reactions conducted in the presence of diluted hydrogen and oxygen, resulting in a 5-fold increase in the yield of benzaldehyde at 30 1C with an AuPd catalyst with secondary porosity. The improvement in rate observed is due to the oxidizing efficacy of in situ generated hydroperoxy species as compared to molecular oxygen alone as the terminal oxidant.