On the Nature of Nitrogen-Containing Groups in the SCR of NO Over Functionalized Activated Coke
2020
Li, Yuran | Lin, Yuting | Cheng, Chungui | Hao, Junke | Zhu, Tingyu
To improve the denitrification efficiency for the selective catalytic reduction of NO with NH₃ in the flue gas purification process, a low-rank activated coke (AC) was treated with ammonia (NH₃·H₂O) solution or nitric acid (HNO₃) solution to increase the content and type of nitrogen-containing functional groups, and then the role of nitrogen-containing functional groups in the reduction of NO was analyzed. The modified AC samples were characterized by N₂ adsorption/desorption to determine the pore structures and by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy to detect the surface functional groups. After modification, the content of oxygen-containing functional groups on the AC surface increased, including quinone, lactone and carboxyl, which are favorable for SO₂ adsorption. Meanwhile, the type and content of nitrogen-containing functional groups on the AC surface changed; these groups fall into two categories: active groups and non-active groups. Before and after the denitrification process, the regular changes in the content of active and non-active groups showed that the active groups with pyrrole-like or pyridine-like structures can promote NO adsorption and then strengthen the denitrification. On the other hand, active groups may be reduced by NH₃ or oxidized by O₂, referring to side reactions, to generate non-active groups such as nitro, nitrate, amine and imine. More importantly, the role of nitrogen-containing functional groups was identified in the denitrification process. This chemical modification method is effective for improving the performance of low-cost AC since the employed chemicals are commercially available.
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