碱金属盐对NH_3选择性非催化还原NO的影响

Effect of Alkali Metal Salts on Selective Non-Catalytic Reduction of NO by NH_3

本文研究碱金属元素Na和K对NH_3选择性非催化还原NO的影响,并组建Na-K-H-O-N详细化学反应机理解释其影响机制。实验表明,碱金属盐将"温度窗口"向低温方向扩展,并在较大温度范围内增加脱氮效率,效果与碱金属盐的种类和碱金属原子浓度几乎无关,但钠盐的作用强于钾盐;高温下碱金属对脱氮的促进作用较小,高浓度碱金属的脱氮效率比低浓度时略高。路径分析显示,NH_2对还原NO起重要作用,OH是促使NH_2生成的关键,Na的加入有利于在低温下促进OH自由基的生成,其主要反应为NaOH+O_2→NaO_2+OH、NaOH+M→Na+OH+M和NaO+H_2O→NaOH+OH。相同形式的含K反应由于较高的活化能和较低的温度指数,反应速率较低,对OH生成的促进作用有限。

The effect of alkali metal elements Na and K on the selective non-catalytic reduction of NO by NH3 was studied, and a detailed mechanism containing Na-K-H-O-N elements was established to explain the effect. The experimental results show that alkali metal salts can extend the ＂temperature window＂ toward a lower temperature, enhance the efficiency of NOχ removal within a large range of temperatures, and the promoting effect is not sensitive to the salt type and atom concentration of alkali metal; however, the effect of sodium is more obvious than that of potassium. Under high temperatures, the promoting effect is not obvious, and higher concentration of alkali metal can enhance it slightly. The reaction path analysis shows that NH2 is important for NO reduction, and OH is crucial for producing NH2. The Na additives are beneficial for OH production under low temperatures, and the main reactions are NaOH＋O2 →NaO2＋OH, NaOH＋M→Na＋OH＋M, and NaO＋H20→NaOH＋OH. The K reactions of the same form with higher activation energy and lower temperature exponent have lower reaction rates; therefore, the promoting effect of potassium on OH production is limited.