Reduction of Lower Concentration NO with Ammonia at Room Temperature over Pitch Based Active Carbon Fibers Calcined and Further Activated with Sulfuric Acid.

Abstract

Reduction of lower-concentration NO (10ppm) with NH3 (20ppm) over pitch based active carbon fibers (p-ACF) at room temperature was examined to find higher activity in humid air, by further activation with H2SO4, after the calcination. The activation with H2SO4 increased the NO conversion from 50% over the as-received ACF by W/F=5×10-3g•min•ml-1 to 63% in the dry air. The increase of the activity in wet air (80% relative humidity), however, remained in the comparatively lower range of 5 to 12%. The calcination at 800°C is effective to increase the conversions to 63% in dry air, and 23% in wet air. The successive activation with H2SO4 was very effective to enhance the activity in wet air, giving a conversion of 40%, although the conversion in the dry air increased conservatively to 68%. The activation with H2SO4 increased the surface oxygen groups, which can enhance the reduction of NO in dry air. Their excess presence, however, does not lead to higher activity in the humid air because such low concentrations of NO and NH3 may require a small number of highly active sites, while inhibition of H2O may be more important. Very sensitive control of functional groups of surface oxygen and extent of graphitization, thus, appear highly influential on the reduction of NO with NH3 at their present lower level of concentrations, in the humid air at room temperature. The calcination prior to the activation by H2SO4 may remove excess oxygen functional groups introduced at activation by steam to enhance hydrophobicity and to control surface reactivity through partial graphitization. Successive activation by H2SO4 may introduce the optimum number and kinds of active sites containing oxygen functional groups.