Highly active catalysts for the photooxidation of organic compounds by deposition of [60] fullerene onto the MCM-41 surface: A green approach for the synthesis of fine chemicals

Abstract

A series of C60 catalysts supported on MCM-41 was prepared in the context of developing a highly active heterogeneous catalytic system for the singlet oxygen-mediated oxidation of organic substrates. Successive incipient wetness impregnation was used for preparing 3, 6, 9 and 12wt.% C60 onto MCM-41 surface. N2 adsorption, FT-IR, XRD, HR-TEM, DRS and TGA, have been used to characterize the photocatalysts.It was found that C60 is highly dispersed (especially in the 3 and 6wt.% C60 catalysts) within the mesopores or on the external surface of MCM-41, as clusters or crystallites/aggregates of very small size and presumably in the form of atomic layers. The mesoporous structure and characteristics (surface area, mesopore size and volume) of MCM-41 remain almost intact upon deposition of C60 on its surface.The photocatalytic activity was assessed in the photocatalytic oxidation of olefins via the singlet oxygen ene reaction by studying the photooxygenation of 2-methyl-2-heptene as a probe reaction. The catalytic tests were carried out at 0–5°C in CH3CN under oxygen atmosphere and using a 300W xenon lamp as the light source. To investigate further the potential applications of our catalysts we examined various types of photooxidations including the [4+2] or [2+2] cycloaddition, the heteroatom oxidation with sulfur or phosphorus containing compounds and the oxidation of phenols.The heterogeneous photocatalysts obtained were proved to be very active exhibiting higher substrate conversion, TON and TOF values, compared to those of the unsupported (solid) C60 and the corresponding photocatalysts supported on silica or γ-alumina. This was mainly attributed to the better dispersion of C60 on the MCM-41. The conversion achieved over the catalysts increases with the amount of the supported C60 up to a value of 6wt.% and then it decreases whereas the TON and TOF values decrease monotonically as the amount of the supported C60 increases following the increase in the size of the supported C60 crystallites/aggregates. Shadow effects were not observed under our experimental conditions.