γ-Alumina-supported [60]fullerene catalysts: Synthesis, properties and applications in the photooxidation of alkenes

Immobilization of [60]fullerene onto γ-Al2O3 surface provides new heterogeneous photocatalysts for the oxidation of organic compounds under oxygen atmosphere. These catalysts have been prepared by simple or successive incipient wetness impregnation (using an organic solvent) followed by air-heating at 180 °C. In the C60/Al2O3 system, C60 loading was varied in the range of 1–4% (w/w). Several experimental techniques including BET, XRD, DRS, TGA, microelectrophoresis, photoluminescence and kinetic extraction, have been used to characterize these catalytic materials. It was found that the quite high surface exposed by the supported C60 increases with the amount of the supported C60, while the dispersion of the supported C60 decreases. The quite stable supported [60]fullerene phase is comprised from C60 clusters, small and large aggregates. This non-uniform size distribution is reflected to a non-uniform distribution concerning the ‘supported phase–support’ interactions. These interactions decrease with the amount of the supported C60. The photocatalysts prepared may be safely used up to 200 °C. Above this temperature the supported C60 is sublimated/combusted in air.The photocatalytic activity of the so-obtained catalytic systems has been evaluated in terms of substrate conversion in the singlet oxygen ‘ene’ reaction of alkenes. The photooxygenation of 2-methyl-2-heptene has been examined as a probe reaction. It was found that the catalytic activity increases with the increasing amount of the supported C60 up to the value of 3% (w/w) and then decreases. The intrinsic activity expressed as TON or TOF decreased monotonically with C60. In all cases, however, the photocatalytic activity of the Al2O3-supported C60 catalysts was substantially increased compared to the unsupported C60 precursor, exhibiting quantitative conversion yields after short reaction times. The catalytic behavior was attributed to the aforementioned opposite trends which follow the surface exposed by the supported C60 on one hand and the ‘supported C60–support’ interactions and the C60 dispersion on the other hand. The easy separation of these solid catalysts from the reaction mixture, the high activity and stability as well as the retained activity in subsequent catalytic cycles, make these supported catalysts suitable for a small-scale synthesis.

Graphical abstractThe immobilization of C60 on the surface of γ-Al2O3 increases considerably its catalytic activity for the photooxidation of alkenes.Figure optionsDownload full-size imageDownload high-quality image (101 K)Download as PowerPoint slide