钾盐对V_2O_5/TiO_2催化剂NH_3选择性催化还原NO反应的影响

Effects of Potassium Salts on Selective Catalytic Reduction of NO With NH_3 Over V_2O_5/TiO_2 Catalysts

钾在中国燃煤和生物质烟气中以钾盐——硫酸钾和氯化钾的形式存在。文中采用静态N2物理吸附、程序升温表面反应(temperature-programmed surface reaction,TPSR)、傅里叶变换红外(Fourier transform infrared,FT-IR)光谱和催化活性评价的方法,研究了钾盐对V2O5/TiO2催化剂上NH3选择性催化还原NO反应的影响。结果表明,钾盐使V2O5/TiO2催化剂活性降低。随着钾盐在催化剂上负载量的增加,稳定的NO脱除温度窗口逐渐变窄,当K与V物质的量之比达到3.0时,该窗口消失。钾盐的掺入使催化剂表面活性位数量明显减少,但是并没有显著改变催化剂的反应性。催化剂失活的主要原因是K优先配位在催化剂表面的Br￠nsted酸性位上,中和了Br￠nsted酸性位酸性,使Br￠nsted酸性位上吸附的氨减少。

Potassium is present in the form of potassium salts, potassium sulphate and potassium chloride, in the flue gas generated by firing the Chinese coal and biomass, respectively. The effects of potassium salts on the selective catalytic reduction of NO with NH3 over V2O5/TiO2 catalysts were studied with static nitrogen physical absorption, temperature-programmed surface reaction （TPSR）, Fourier transform infrared （FT-IR） spectroscopy and activity measurements. The results show that potassium salts deactivate the V2O5/TiO2 catalysts. And the stable temperature window of NO removal gradually narrows with increasing sediment of potassium salts on the catalysts and eventually disappears when the molar ratio of K to V reaches 3.0. The potassium salts doped on the catalysts markedly reduce the number of active sites on their surfaces but not change their reactivity significantly. The main reason of the catalyst deactivation is that K preferentially coordinates to Brcnsted acid sites on the catalysts＇ surfaces and neutralizes the acidity of them, as a result, the adsorbed NH3 decreases.