The aerobic oxidation of 5-hydroxymethylfurfural (HMF) with homogeneous Co(OAc)2/Zn(OAc)2/Br−, and heterogeneous Au–TiO2 and Au–CeO2 nanoparticulate catalysts was carried out in acetic acid with and without a trifluoroacetic acid (HTFA) additive. The selectivity of the oxidation products, 2,5-furandicarboxylic acid (FDCA) and 5-formyl-2-furancarboxylic acid (FFCA), improved in the presence of the HTFA (1 wt%) additive. The homogeneous oxidation catalyst gave higher selectivity for FDCA (60% yield) under 1 atm of O2 at 90 °C while Au–TiO2 afforded 80% FFCA under the same conditions.