The wet ammonia desulphurization process can be retrofitted to remove NO and SO2 simultaneously by adding soluble cobalt (II) salt into the aqueous ammonia solution. The hexamminecobalt (II), Co(NH3), is the active constituent in the removal of nitric oxide with the hexamminecobalt ammonia solution. To maintain the capability of removing NO with the hexamminecobalt solution, activated carbon is used to catalyze the reduction of hexamminecobalt (III) to hexamminecobalt (II). In this study, the study on the investigation into the intrinsic kinetics of the hexamminecobalt (III) conversion has been performed. The reduction of hexamminecobalt (III) catalyzed by coconut activated carbon has been studied in a batch stirred cell without the external or internal mass transfer resistances. The experimental results show that the reaction rate increases with the activated carbon mass and the concentration of hexamminecobalt (III). pH affects the reaction greatly. A best Co(NH3)63+ conversion is obtained at pH of 2.74. A high temperature is favorable to such reaction. The reaction is first order with respect to Co(NH3)63+. The intrinsic activation energy of 56.73 ± 1.82 kJ mol−1 has been obtained. A kinetic model for such catalytic reaction can be expressed as follow: © 2009 American Institute of Chemical Engineers Environ Prog, 2010