Sumitomo Chemical has developed a low energy consuming and green process for the catalytic oxidation of HCl to Cl2, especially when compared with the electrolysis process. The RuO2/rutile-TiO2 catalyst has high catalytic activity and thermal stability due to ultra-fine RuO2 crystallites that cover the surface of the TiO2 primary particles with strong interaction. In addition, the silica modified RuO2/rutile-TiO2 catalyst shows higher thermal stability by preventing the RuO2 sintering due to using dispersed SiO2 particles. With these catalysts, high reaction rates required for industrial applications are achieved, even at low temperatures.