The effect of the oxidation method of an activated carbon on the selective catalytic reduction of NO_x with NH₃ over CeO₂/activated carbon catalysts

An activated carbon (AC) was oxidized with air at 300℃ for 4 h or with 30 wt% HNO₃ at 60℃ for 4 h under reflux before it was loaded with CeO₂ by an impregnation method to prepare CeO₂/AC catalysts for the selective catalytic reduction of NO_x in flue gas with NH₃. The influence of the oxidation method on the performance of the catalysts was investigated. Both catalysts were characterized by FTIR, N₂ adsorption, XRD, temperature-programmed desorption of NH₃ and temperature-programmed reduction with H₂. Results showed that the HNO₃ oxidation increased both the number of oxygen functional groups and the surface acidity of the AC and the redox activity of the CeO₂/AC-HNO₃, which favored the adsorption and activation of NH₃ with the CeO₂/AC-HNO₃ and hence its catalytic performance. The onset and full conversion temperatures of NO_x over the CeO₂/AC-HNO₃ catalyst were 75 and 190℃, respectively, which were significantly lower than those over the CeO₂/AC-air catalyst. However, the activity of the CeO₂/AC-HNO₃ catalyst was easily inhibited by H₂O.