Adsorption and adsorbed species of SO 2 in humid air during its oxidative removal were studied over pitch-based activated carbon fibers (ACFs) to clarify the reaction scheme of continuous removal of SO 2 , influence of reaction variables, and origin of activity enhancement by the calcination in inert atmosphere. The temperature-programmed desorption of SO 2 adsorbed species suggests that when both oxygen and water were present, the main species on ACF was hydrated SO 3 (H 2 SO 4 ), which desorbed in the form of SO 2 around 300°C, and that the presence of both increased the amount of species by oxidizing and hydrating the adsorbed SO 2 , which desorbed around 60°C without oxidation and 200°C with oxidation but without hydration. The amount of adsorbed H 2 SO 4 over ACF stayed at the same level after 25 h of reaction by balancing elution and adsorption of H 2 SO 4 to allow the steady removal of SO 2 . More water enhanced the adsorption of SO 2 at the initial stage but reduced the amount of adsorbed H 2 SO 4 at the steady state, eluting out H 2 SO 4 faster than the adsorption of SO 2 to keep more active sites open over ACF at the steady state. Hence, complete removal was achieved. A higher calcination temperature significantly increased the rate and amount of both oxidative and oxidative/hydrating adsorption, explaining the largest activity of ACF calcined at 1100°C. The amounts of adsorbed SO 2 and evolved CO from OG-20As by calcination at 500-1000°C are well correlated, indicating that the evolved CO creates an adsorption site on the ACF surface. A similar but different correlation was obtained among ACFs of different surface areas calcined at different temperatures.
Catalytic activities of a series of pitch based active carbon fibers (ACFs) were examined for the reduction of NO (10 ppm) with NH3 (20 ppm) at 293 K. A particular ACF of 840 m2 g−1 surface area exhibited the excellent activities after the calcination at 1123 K, providing conversions of 75 and 47 % in dry and wet (80 % relative humidity) air, respectively, at W/F of 5 × 10−3 g min ml−1. The ACF of the largest surface did not show the largest activity.
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