活性焦催化氧化脱除低温烟气中NO的性能及机理

随着国家环保标准越来越严格，针对典型燃煤工业锅炉排烟温度低，烟气量小特点，为了满足烟气NOx超低排放要求，催化氧化脱硝是理想的技术。为了研究活性焦催化氧化脱除低温烟气中NO的性能及机理，利用固定床反应装置研究70~110 ℃低温烟气活性焦催化氧化脱硝过程，考察温度、烟气中O2对脱硝的影响。此外，通过解析活性焦77 K条件下N2吸/脱附等温线获得其孔径分布及比表面积、利用XPS表征活性焦炭基质及表面化学特性、应用TPD获取反应前后活性焦升温脱附曲线，研究活性焦催化氧化脱硝及活性焦热再生机制。结果表明:70~110 ℃内，温度越低活性焦催化氧化脱硝的性能越好;活性焦催化氧化脱硝初始阶段，逸出的少量NO2来自于NO和活性焦表面多聚芳环边缘的碱性含氧官能团C〖CDS1〗O反应;活性焦表面酸性含氧官能团抑制NO的吸附，而炭基质多聚芳环是构成炭基质的主要物质，其π键提供电子促进催化脱硝;无O2条件下NO作为电子受体占据吸附位，O2存在时由于O2获得π键提供的电子形成反应中间体，与NO生成NO2。活性焦催化氧化NO最终可达到低温烟气脱硝的目的，然而,由于活性焦中碳的还原作用，热再生并不能将活性焦催化氧化生成的NO2脱附，而是以NO的形态伴随着CO2脱附下来。

Removal of NO from low temperature flue gas by catalytic oxidation over activated coke:Performance and mechanism

With the China’s increasingly stringent environmental standards,catalytic oxidation denitrification is an ideal 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 isotherm 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 oxidation and thermal regeneration of activated coke for denitrification.The results show that with the decrease of temperature 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〖CDS1〗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 electron 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.