Heterogeneous wheel-shaped Cu20-polyoxotungstate [Cu20Cl(OH)24(H2O)12(P8W48O184)]25- catalyst for solvent-free aerobic oxidation of n-hexadecane.

The selective oxidation of alkanes as a green process remains a challenging task because partial oxidation is easier to achieve with sacrificial oxidants, such as hydrogen peroxide, alkyl hydroperoxides or iodosylbenzene, than with molecular oxygen or air. Here, we report on a heterogeneous catalyst for n-hexadecane oxidation comprised of the wheel shaped Cu20-polyoxotungstate [Cu20Cl(OH)24(H2O)12(P8W48O184)]25- anchored on 3-aminopropyltriethoxysilane (apts)-modified SBA-15. The catalysts were characterized by powder X-ray diffraction (XRD), N2-adsorption measurements and Fourier transform infrared reflectance (FT-IR) spectroscopy. The heterogeneous Cu20-polyanion system catalyzed the solvent-free aerobic oxidation of n-hexadecane to alcohols and ketones by using air as the oxidant under ambient conditions. The catalyst exhibits an exceptionally high turn over frequency (TOF) of 20,000 h(-1) at 150 degrees C and is resistant to poisoning by CS2. Moreover, it can be easily recovered and reused by filtration without loss of its catalytic activity. Possible homogeneous contributions also have been examined and eliminated. Thus, this system can use air as oxidant, which, in combination with its good overall performance and poison tolerance, raises the prospect of this type of heterogeneous catalyst for practical applications.