Simultaneous removal of NO and elemental mercury from coal-fired flue gas using natural ferruginous manganese ore at low temperature

Abstract

• Ferruginous manganese ore (FMO) was developed for NO and Hg 0 removal from flue gas. • FMO was directly adopted as a SCR catalyst without need for calcination treatment. • FMO exhibited excellent catalytic activity for NO and Hg 0 removal at 200 °C. • Mn 4+ , Fe 3+ , and lattice oxygen served as active sites for NO and Hg 0 removal. Natural ferruginous manganese ore (FMO) was developed as a cost-effective NH 3 -SCR catalyst for the simultaneous removal of NO and elemental mercury (Hg 0 ) from coal-fired flue gas. The chemical composition, pore structure, crystal structure and surface chemistry of FMO were characterized by different methods. The results showed that FMO was constructed with sheet-like structures. There were massive slit-shaped pores in the FMO. Manganese and iron oxides existed in an amorphous form. After calcination, the NO removal performance of FMO was obviously decreased due to the decomposition of MnO 2 . A high NH 3 /NO ratio was conductive to NO removal but excessive NH 3 was unnecessary for NO removal. NO could promote Hg 0 removal whereas Hg 0 had little effect on NO removal. The effects of different SCR atmosphere (inlet, middle layer, and outlet), reaction temperature (100 °C–400 °C), and flue gas composition (O 2 and SO 2 ) on NO/Hg 0 removal was also studied. At the optimal temperature (200 °C), the NO removal efficiency was greater than 80% and the Hg 0 removal efficiency was close to 100%. To some extent, FMO presented preferable SO 2 poisoning resistance probably because of the presence of iron oxide. The mechanism of NO/Hg 0 removal over FMO was further described. Both fast SCR and conventional SCR reactions happened over FMO during NO removal. Mn 4+ , Fe 3+ , and lattice oxygen were first consumed and then replenished by gaseous O 2 . FMO served as a catalyst for Hg 0 oxidation during a long period of denitration process.