Selective hydrodehalogenation of a variety of aromatic halides (e.g., halogen subsitute phenones and hexafluorobenzene) using isopropanol as the hydrogen source was successfully achieved over supported Au nanoparticles. Distinct reaction pathways were established based on kinetic analysis and intermediate identification. Surface hydrides generated by isopropanol oxidation mediate the hydrodehalogenation by nucleophilic attack without the involvement of carbon centered radical. On the other hand, engeretic electrons on Au nanoparticles populated by visible light irradiation trigger the dissciation of carbon halogen bond (C-X) by injection to the substrates' lowest unoccupied molecular orbitals (LUMO). The super-linear dependency on light intensity, shape of the action spectrum and formation of aryl radical revealed that electron transfer dominates the hydrodehalogenation process, which features a significantly lower activation barrier than transfer of surface hydride. The observed activity is correlated to energy levels of the substrate electron accepting states.