Effects of pretreatment of Pd/AC sorbents on the removal of Hg0 from coal derived fuel gas

• Hg0 removal efficiency of the untreated 1Pd/AC sorbent was higher than that of the O2 or H2 pretreated sorbents.
• H2 atmosphere had a significant effect on the Hg0 removal efficiency of 1Pd/AC sorbents.
• Elemental Pd is the active species for Hg0 removal over Pd/AC sorbents.

The Pd supported activated carbon (Pd/AC) sorbents were pretreated by 5 vol.% O2 or H2, and the Hg0 removal efficiency of the corresponding sorbents was compared in different atmospheres. X-ray photoelectron spectroscopy, X-ray diffraction and X-ray absorption spectroscopy were employed to analyze the sorbents at different stages. These results indicated that the Hg0 removal efficiency of the untreated 1Pd/AC sorbent was higher than that of the pretreated sorbents. The efficiency of Hg0 removal from coal derived fuel gas is much higher in N2–H2S–Hg–H2 atmospheres than that in N2–H2S–Hg atmospheres and it can be maintained at about 91.4% for 360 min. There exist three types of Pd forms over Pd/AC sorbent, i.e. Pd0, Pd2 + and Pd2H, and among which Pd0 is the active species for Hg0 removal over Pd/AC sorbent. H2 can promote the Hg0 removal due to the in situ reducing of palladium oxide in the process of sorbent evaluation. H2 and O2 in the pretreated atmosphere suppressed the Hg0 removal due to the formation of inactive palladium hydride and easily sulfidized palladium oxide, respectively, and then the decrease of Pd0 content.

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