This research aimed to achieve HCl removal for chlorine-containing hot coal gas by using supported oxide sorbents in a fixed-bed reactor at 673–873 K. Mn2O3/SiO2 was chosen as the optimal sorbent to eliminate chlorine species, after thermodynamic screening of the dechlorination potential of sorbents based upon various metals. The dechlorination experiments and results of the ICP, BET, XRD, XPS, and FTIR analyses provided in-depth views of the reaction chemistry behind the complex system of HCl removal in a simulated syngas containing 3,000 ppm HCl, 25 vol% CO, 15 vol% H2, and N2. When the sorbent composed of 23 wt% Mn2O3/SiO2 came into contact with HCl, CO, and H2, the reaction mechanism contained two paths. At lower temperatures Mn2O3 tended to react with HCl, while at higher temperatures it might first be reduced into Mn3O4 and then react with HCl. The probable products from the reaction (Mn2O3 and HCl or Mn3O4 and HCl) are MnCl2, Cl2, and H2O. That is, as the reaction temperature increased, the second path started to become more important. The final product of this reaction might also include metallic manganese in addition to MnCl2. Furthermore, when the temperature increased, the equilibrium constants of all the reactions reduced, and subsequently resulted in the decreasing sorbent performance.