Reaction of NO₂ in air at room temperature with urea supported on pitch based activated carbon fiber

Reactivity of NO₂ in air with urea supported on pitch based activated carbon fiber (ACF) was examined by its concentration from 50 to 1000 ppm at room temperature to establish a basic scheme for its reduction in an open atmosphere. NO₂ was found to be reduced into N₂ with urea supported on the ACF and its reduction continued until the complete consumption of urea. A small amount of NO was liberated during at the same time. The conversion of NO₂ appears to depend on the amounts of both urea and the ACF, although too much concentration of urea on ACF of limited amount decreased the NO₂ conversion. O₂ concentration in air was not influential on the reduction of NO_2, whereas humidity accelerated the formation of HNO₃ over the ACF, resulting in the extension of NO₂ removal period. The constant conversion of NO₂ was obtained regardless of NO₂ concentration, effective reduction of very low concentration of NO₂ being expected. Following reactions are suggested to take place over the ACF:2NO₂→NO ₃ad+NO(disproportionation);NO₂+NO+(NH₂) ₂CO→2N₂+CO₂+2H₂O;NO ₃ad+(NH₂)₂CO→1.5N₂+CO ₂+2H₂O;being summed up as the following overall reaction:6NO₂+4(NH₂)₂CO→7N ₂+4CO₂+8H₂O.Approximately 1.8 molecules of NO₂ were reduced by one molecule of urea except for the following reaction:NO₂+NO₃ad+H₂O→2HNO ₃↓Through above reaction, NO₂ was removed as nitric acid.