Deposition of fullerene C₆₀ on the surface of MCM-41 via the one-step wet impregnation method: Active catalysts for the singlet oxygen mediated photooxidation of alkenes

A series of C₆₀ catalysts supported on MCM-41 was prepared for the singlet oxygen-mediated oxidation of alkenes to the corresponding hydroperoxides (ene or Schenck reaction). The one-step wet impregnation method, followed by heating at 180 C, was used for dispersing effectively 6, 9 and 12 wt% C₆₀ onto the MCM-41 surface. N₂ adsorption-desorption measurements, FT-IR, XRD, DRS and TGA were used to characterize the prepared photocatalysts. The photocatalytic activity of the C₆₀/MCM-41 series was determined by using the photooxygenation of 2-methyl-2-heptene as a probe reaction. The results of the present study were compared with those obtained in our previous studies where the same photocatalysts had been prepared by using the successive wetness impregnation method. It was found that very effective C₆₀/MCM-41 photocatalysts can be synthesized by applying the one-step wet impregnation method. All three photocatalysts exhibited similar activity in terms of substrate conversion, whereas their intrinsic activity which is expressed by the TON or TOF values, decreased with increasing C₆₀ content. The replacement of the successive incipient wetness impregnation by the simpler wet impregnation method provokes an increase in the photocatalytic activity of the samples with C₆₀ content equal to 9 and 12 wt% but it does not affect the photocatalytic activity of the sample with C₆₀ content equal to 6 wt%, which exhibits the maximum intrinsic activity. The influence of the deposition method and the C₆₀ loading on the photocatalytic performance of the C₆₀/MCM-41 catalysts was rationalized on the basis of the different size of the supported C₆₀ crystallites.