Reduction of Low Concentration NO with NH3 at Ambient Temperatures over Pitch Based Active Carbon Fibers Further Activated with Sulfuric Acid

Abstract

Catalytic reduction of low concentration NO (10 ppm) with NH3 (20 ppm) was studied at the ambient temperatures (0-50 °C) over pitch based active carbon fiber (ACF) further activated with sulfuric acid. A fiber of the lowest surface area among the ACFs showed a significant activity in dry air, providing NO (10 ppm) conversion of 59% with 20 ppm NH3at 10 °C by WIF=5x 10-8 gmin/m/. Humidity in the air decreased very severely the activity, the lower reaction temperaure emphasizing the retardation, although non-trivial activity (NO conversion, 13 and 2% respectively) was still observed even at 22 and 0 °C under 100%humidity. Large WIF increased the conversion according to the first order kinetics. A slight heating up of the wet feed gas was very effective to increase the conversion comparable to that in dry air by decreasing the relative humidity at the reaction temperature. Humidity was found to severely reduce the adsorption of NO, the adsorption of NH3 being slightly influenced. The catalysis at 20 °C appeared to follow the Langmuir equation in a concentration range of 10 to 400 ppm of the reactant gases in both dry and wet air where the reaction order in NO was always first regardless of its concentration, while that in NH3 varied from first to zero, reflecting its concentration. The catalytic activities of ACFs and their further activated forms under variable conditions were correlated to the amount of evolved CO, at a temperature range of 200-450 °C in Temperature Programmed Decomposition Analyses. Two separate lines were obtained with the activities in wet and dry air, suggesting that the CO, giving acidic site on the ACFs is a common active site for the catalysis regardless of humidity, which reduces the effective number of the site through retarding the adsorption of both reactants. Polar ammonia may suffer less retardation of its adsorption by humidity.