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

Abstract

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 12wt% 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 12wt% but it does not affect the photocatalytic activity of the sample with C60 content equal to 6wt%, 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.