In-situ grown Co3O4 nanoparticles on wood-derived carbon with natural ordered pore structure for efficient removal of Hg0 from flue gas

Abstract

Sorbent morphology is significant to Hg0 removal performance due to its serious impacts on the number and availability of adsorption sites and the mass transfer of the Hg0 removal process. Given this, a novel sorbent was obtained by in-situ growth of Co3O4 nanoparticles on channel walls of wood vessel which has regular mesoporous channels. The effects of synthetic conditions of hydrothermal temperature and NH4F concentration on sorbent morphology and Hg0 removal performance are investigated. Characterization results show that Co3O4 nanoparticles integrate a monolithic shell as synthesis temperature rises, while the nanoparticles grow radially with the increase of NH4F concentration. Radial growth of nanoparticles results in a higher crystallinity. The sorbent synthesized at hydrothermal temperature of 90 °C with the NH4F concentration of 0.05 M (denoted as T90C0.05) has uniform Co3O4 nanoparticle size, homogeneous dispersion and a larger specific surface area. Furthermore, T90C0.05 has a higher chemisorbed oxygen concentration and a higher Co3+/Co2+, which is of benefit to Hg0 removal process. Therefore, T90C0.05 has an excellent Hg0 removal efficiency of 97% with a high gas hourly space velocity of 180, 000 h−1 at 200 °C and the Co3O4 loading is only wt.5%. The effects of compounded flue gas components on the Hg0 removal performance were also studied. NO can weaken the inhibition effect of NH3 through the reaction between NO and NH3 forming labile [NH2NO]. In contrast, SO2 can not weaken the inhibition effect of NH3 due to the production coming from the reaction of SO2 and NH3 is stable at Hg0 removal temperature.