The selective hydrodechlorination of tetrachloromethane (CCl4) was performed over supported platinum-gallium catalysts with a support of MgF2 to improve CHCl3 selectivity and catalytic stability. In order to better understand the behavior of the Ga and MgF2 support, hydrogen chemisorption, temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) measurements were conducted to characterize the catalysts. It was found that the electron-deficient Pt species are formed on the catalyst surface during the hydrodechlorination reaction due to the adsorption of active chlorine. The addition of Ga into the catalysts results in forming Pt-Ga assemblies such as PtGa alloys on the catalyst surface, and generates a Pt-Ga interaction as confirmed by TPR and XPS. The Ga addition will significantly increase the dispersion of Pt and create more Pt sites exposed to the reaction atmosphere on the catalyst surface in effect. The influence of Ga on the CHCl3 selectivity and the conversion of CCl4 can be ascribed to the modification of Ga to the electronic properties of the Pt active sites by changing the electronic environment surrounding the Pt atoms via the Pt-Ga interaction. The modified Pt species are believed to be beneficial to form a fast desorption step for the adsorbed *CCl3 species (a commonly accepted precursor to generate CHCl3) under the assistance of hydrogen. The adsorption of reactant CCl4 will be weakened on the catalyst surface and cause a lower conversion of CCl4 (c) 2005 Elsevier B.V. All rights reserved.