Understanding of selective base-free oxidation of glycerol to dihydroxyacetone (DHA) over Pt-based catalysts is of paramount scientific and industrial importance. In this work, a comparative study between differently sized SbOx-promoted and unpromoted Pt/CNTs catalysts is carried out to decouple the promoter effects from the metal size effects. The introduction of SbOx appears to enhance both the glycerol oxidation activity and the DHA selectivity, and the largely sized promoted Pt/CNTs catalysts afford a relatively high DHA yield and less C-C bond cleavage. X-ray photoelectron spectroscopy measurements reveal that the Sb species are mainly in the form of SbOx, and the differently sized promoted catalysts show similar metal binding energies. Furthermore, theoretical studies on the promotional effects of SbOx are carried out by DFT calculations. It is found that the presence of the promoter on the catalyst surface favors the preferential activation of the secondary hydroxyl group. (C) 2018 American Institute of Chemical Engineers