Aerobic oxidation of α-pinene catalyzed by carbon nanotubes

Abstract

Carbon nanotubes (CNTs) and nitrogen-doped CNTs (NCNTs) as metal-free catalysts exhibited an excellent activity in the selective oxidation of α-pinene with molecular oxygen as the terminal oxidant. Two distinct pathways, i.e. epoxidation and allylic oxidation, were active in this reaction. Enhancement of epoxidation was observed over CNTs, yielding the highest epoxidation/allylic oxidation products ratio. Excellent activity was achieved over NCNTs, giving 54.5% α-pinene conversion and 272.4 mmol g⁻¹ h⁻¹ mass-normalized activity, which compete with that of the state-of-the-art metal catalysts. Allylic oxidation was enhanced over NCNTs, using which equimolar amounts of epoxide and allylic products were produced. Thus, N-doping boosted the overall conversion and the yields of both epoxidation and allylic oxidation products, which was supported by the results of theoretical simulation.