Experimental and theoretical analysis of elemental mercury removal from syngas over Fe-Ti spinel

A magnetic Fe-Ti spinel sorbent was synthesized by the co-precipitation method and applied to remove gaseous Hg-0 from syngas. A superior Hg-0 removal performance was achieved in the temperature range of 120-180 degrees C, and the highest an average removal efficiency of was approximately 95% at 150 degrees C under simulated syngas. H2S was adsorbed on the Fe-Ti spinel surface,which generated active sulfur species, and enhanced the Hg-0 removal efficiency significantly. CO, H-2 and H2O variably suppressed the Hg-0 removal performance. H2S-pretreatment, X-ray photoelectron spectroscopy (XPS) and Hg-0-temperature programmed desorption (Hg-0-TPD) results demonstrated that Hg-0 reacted with H2S over Fe-Ti spinel followed the Eley-Rideal mechanism, in which gas-phase Hg-0 reacted with the active surface sulfur species generated from H2S oxidation and formed surface-bonded HgS. The surface Fe3+ and surface-active oxygen species were involved in the H2S and Hg-0 adsorption and transformation process. Stability and regeneration cycling experiments indicated that Fe-Ti spinel exhibited excellent stability for Hg removal and great regeneration ability. Density functional theory (DFT) calculations showed that H2S underwent strong chemisorption on the Fe-Ti spinel surface with an adsorption energy of 116.988 kJ/mol, and then H2S further dissociated on the sorbent surface to generate active sulfur species, which reacted strongly with gas-phase Hg-0 to form HgS.

Automated summary

A magnetic Fe-Ti spinel sorbent synthesized by the co-precipitation method showed superior performance in removing gaseous Hg-0 from syngas. The presence of H2S on the surface of Fe-Ti spinel generated active sulfur species, leading to enhanced Hg-0 removal efficiency. CO, H-2, and H2O had varying degrees of suppression on Hg-0 removal performance. The reaction between Hg-0 and H2S on the Fe-Ti spinel surface followed the Eley-Rideal mechanism and formed surface-bonded HgS. Fe3+ and surface-active oxygen species played important roles in the adsorption and transformation process of H2S and Hg-0. The Fe-Ti spinel exhibited excellent stability and regeneration ability in Hg removal.