The promoted effect of Cu(NO3)(2) on aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) catalyzed by VOSO4 in acetonitrile was intensively investigated. It was revealed that Cu(NO3)(2) facilitated the activation of VOSO4 to generate active V5+ species via the generation of NO gas. The high OFF selectivity is ascribed to Cu2+ cation which can effectively prohibit oxidative C-C bond cleavage reaction of HMF and prevent radical reaction of OFF to humins. In addition, the polarity of solvent plays a great role on high selectivity of OFF. (C) 2014 Elsevier B.V. All rights reserved.