Aerobic oxidations of α-pinene over cobalt-substituted polyoxometalate supported on amino-modified mesoporous silicates

Abstract

Co-containing polyoxometalate [Bu 4N] 4H[PW 11Co(H 2O)O 39] (Co-POM) was supported on various NH 2-modified mesoporous silicate matrixes (SBA-15, MCF, and SiO 2-xerogel). The catalysts were characterized by elemental analysis, N 2 adsorption, DRS–UV, and FTIR spectroscopy. α-Pinene autoxidation and its co-oxidation with isobutyraldehyde (IBA) over the supported Co-POM catalysts have been studied and compared with the corresponding processes in the presence of the homogeneous Co-POM. The autoxidation process affords allylic oxidation products, the selectivity to verbenol/verbenone decreases with alkene conversion and attains 70% at 20% conversion and 40% at 46% conversion. The catalysts can be used repeatedly without loss of the activity and selectivity during several catalytic cycles. Co-oxidation of α-pinene and IBA produces selectively α-pinene epoxide with up to 94% selectivity at 96% alkene conversion. The catalysts can be regenerated by evacuation.