HCN and N₂ formation mechanism during NO/char reaction

The reaction of phenol/formaldehyde resin char with NO was carried out in the temperature range from 850 to 1100 °C. Nitrogen-containing species formed during the reaction were carefully examined by a high-speed gas chromatograph and a mass spectrometer. Large amounts of N₂ and CO and small amounts of CO₂ and N₂O were formed by the NO/char reaction. In addition to these products, a significant amount of HCN was observed in the high-temperature region. The mechanism of HCN formation behavior was examined by step response experiments. It was found that HCN was formed through nitrogen-containing surface species on char, C(N), and its formation rate was greatly affected by the amount of available hydrogen. The N₂ formation was also affected by the amount of available hydrogen in the following manner. N₂ was formed mainly by the reaction of C(N) with gaseous NO. However, a part of C(N) was consumed through the conversion to HCN if sufficient hydrogen was present in the vicinity of C(N). When the HCN formation took place, the amount of C(N) decreased, leading to less N₂ formation. Thus, it is suggested that even in the char-related reaction, hydrogen content is an important factor for the fate of nitrogen.