Abstract:
With the China’s increasingly stringent environmental standards,catalytic oxidation denitrification is an ide- al technology aiming at the characteristics of low exhaust temperature and small amount of flue gas in typical coal-fired industrial boilers for meeting the requirement of ultra-low NOx emission in flue gas. In order to study the performance and mechanism of catalytic oxidation of activated coke for removing NO in low-temperature flue gas and provide some theo-retical basis for the development of related technologies,the process of removal of NO from low temperature flue gas in the range of 700-110 ℃ by catalytic oxidation over activated cokes was studied with a fixed bed reactor,and the effects of temperature and presence of O2 in flue gas were investigated. Besides,the pore size distribution ( PSD) and BET specific surface area of activated coke were obtained by the data analysis of N2 adsorption / desorption iso- therm at 77 K,and the carbon matrix and surface chemistry of virgin or / and spent activated coke samples were charac- terized by XPS and temperature program desorption (TPD) with the aim to elucidate the mechanism of catalytic oxida- tion and thermal regeneration of activated coke for denitrification. The results show that with the decrease of tempera- ture between 70-110 ℃ ,the catalytic activity of activated coke for catalytic oxidation NO is enhanced. In the initial stage of catalytic oxidation denitrification of activated coke,a small amount of NO2 comes from the reaction of NO and basic ox-ygen-containing functional group C O at the edge of polycyclic aromatic rings on the surface of activated coke. Acidic oxygen functional groups on surface of activated coke will inhabit NO chemisorptions while the π bond e- lectron of polycyclic aromatic rings as main substance consti-tuting the carbon matrix can be easily transferred to the adsorbed species which will promote cat-alytic denitrification. Being electron acceptor,NO will occupy adsorption site in absence of O2 ,meanwhile,O2 will form intermediate by accepting electron from π bond that will react with NO and generate NO2 in the presence of O2 . Catalytic oxidation of NO by activated coke can achieve the goal of denitrification of flue gas at low temperature. However,during the thermal regeneration it is the NO coupled with CO2 rather than NO2 that desorbs from activated cokes due to the reduction effect of carbon element in activated coke.