采用程序升温脱附、在线质谱和原位漫反射红外光谱等手段,比较了NO和NO_2在V_2O_5及V_2O_5/AC催化剂表而的选择催化还原(SCR)反应行为.结果表明,氨以质子态NH_4~+和共价态NH_3分子两种形态吸附于纯V_2O_5表面,V=O为氨的主要吸附活性位.无氧状态下,NO和NO_2皆可与吸附于V_2O_5表面的NH_3反应,并且NO_2与吸附态NH_2的反应活性高于NO.但在V_2O_5/AC催化剂表面,同样在无氧条件下,NO几乎不与吸附态NH_3反应,而NO_2却可以反应并生成N_2.在V_2O_5/AC表面,NO很容易被气相O_2氧化为NO_2,然后参与SCR反应.可见,NO_2是NO在V_2O_5/AC表面发生SCR反应的中间体.
Temperature-programmed desorption, on-line mass spectroscopy, and in situ diffuse reflectance infrared Fourier transform spec-troscopy were preformed to study selective catalytic reduction (SCR) of NO and NO_2 with NH_3 over V_2O_5 and activated carbon (AC)-supported V_2O_5 (V_2O_5/AC). The results show that both protonated (NH4+) and molecularly coordinated (NH_3) ammonia species form on the V_2O_5 surface and V=O bond is the primary active site. Both NO_2 and NO can react with the adsorbed ammonia in the absence of oxy-gen, but the activity of NO_2 is superior to that of NO. On the V_2O_5/AC surface, NO_2 still can react with the adsorbed NH_3 species to form N_2, but NO shows little activity unless oxygen is present. SCR of NO on V_2O_5/AC proceeds through oxidation of NO to NO_2 by oxygen on the AC surface followed by reaction of NO_2 with NH_3 species adsorbed and activated on the V_2O_5 surface .
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