Tunning active oxygen species for boosting Hg0 removal and SO2-resistance of Mn-Fe oxides supported on (NH4)2S2O8 doping activated coke

Abstract

Active oxygen species (AOS) play an essential role in modulating the activity of activated coke (AC) based samples. In this paper, AC was endowed with abundant AOS by modifying with (NH4)2S2O8 and MnOx-FeOx for Hg0 removal. (NH4)2S2O8 treatment induced abundant micropores and oxygen-containing functional groups, and thus provided more anchoring sites for the dispersion of MnOx-FeOx. The synergy of MnOx-FeOx and interaction between MnOx-FeOx and NAC support contributed to a larger surface area, highly-dispersed active components, stronger reducibility, and more metal ions with high valence of MnFe/NAC. The optimal MnFe/NAC exhibited superior Hg0 removal efficiency above 90% at 120∼180 ℃, as well as excellent performance for simultaneous removal of Hg0 and NO, and 600 ppm SO2 and 8 vol.% H2O addition led to a slight deterioration. XPS and Hg-TPD revealed that mercury adsorbed on MnFe/NAC included phy-Hg, C=O-Hg, COO-Hg, and OL-HgO. Besides, the priority of AOS for Hg0 chemisorption was C=O > COO- > OL, and Hg2+ was also detected in the outlet. Moreover, the SO2-poisoning effect was ascribed to the sulfation of MnOx and the occupation of COO- and C=O, and FeOx incorporation enhanced the SO2-resistance through weakening SO2 adsorption on C=O and COO-. The motivation of O2 mainly contributed to the regeneration of AOS, especially OL. The excellent regeneration performance and stability further affirmed the application potential of MnFe/NAC for Hg0 capture from coal-fired flue gas.