Ag doping Fe-Ti spinel sorbent for Hg0 removal from syngas and the mechanism investigation. (15th January 2023)

• Record Type: Journal Article
• Authors: Zhang, Xiaoyang; Xing, Xiangwen; Cui, Lin; Sun, Pengxiang; Tang, Jiyun; Chen, Juan; Dong, Yong
• Is Part Of: Fuel. Volume 332(2023)Part 1
• Publication Date: 2023-01-15
• Subjects: Hg0 removal -- Syngas -- H2S -- Ag/Fe-Ti spinel -- Reaction mechanism -- Density functional theory; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2022.125926
• Languages: English
• ISSNs: 0016-2361

Abstract

Graphical abstract: Highlights: Ag/Fe-Ti spinel presented higher than 90% Hg 0 capture efficiency at 250 °C. H2 S was an effective syngas component responsible for Hg 0 removal. Ag enhanced the Hg 0 removal performance at 250 °C without sulfur poisoning. Hg 0 removal over Ag/Fe-Ti spinel followed the Langmuir-Hinshelwood mechanism. HgS and surface sulfur were formed on the surface of spent Ag/Fe-Ti spinel. Abstract: A series of Ag doping Fe-Ti spinel sorbents (Ag/Fe-Ti spinel) were synthesized using co-precipitation and impregnation methods and employed to remove elemental mercury (Hg 0 ) from syngas at high temperatures (200–350 °C). The role of H2 S on Hg 0 elimination over Ag/Fe-Ti spinel and the Hg 0 removal mechanism were systematically investigated by experimental and theoretical methods. N2 adsorption–desorption, SEM-EDS, XRD, H2 -TPR and XPS were used to characterize the physicochemical properties of samples. The synthesized Ag/Fe-Ti spinel was tested on a fixed-bed reactor for Hg 0 removal from the simulated syngas and showed an average mercury removal efficiency above 90 % at 250 °C. Loading Ag effectively enhanced Hg 0 removal activity in high-temperature syngas by generating Ag-Hg alloy via the amalgamation reaction. H2 S played the most important role in mercury removal, by adsorbing Hg 0 on Ag/Fe-Ti spinel sorbent surface to form active sulfur species. H2 S-pretreatment experiments indicated that the reaction of H2 S and Hg 0 occurred via the Langmuir-Hinshelwood mechanism. Stability and cyclic regeneration experiments indicated that the Ag/Fe-Ti spinel had good regeneration performance and reusability. Density functional theory (DFT) calculation was performed to elucidate that strong chemisorption for H2 S and HgS occurred over the Ag/Fe-Ti spinel surface with adsorption energies of −300.35 kJ/mol and −408.12 kJ/mol, respectively. XPS and DFT calculations demonstrated the Hg 0 removal mechanism, which the chemisorbed Hg 0 reacted with active sulfur species to generated surface-bound HgS. Both XPS and Hg 0 -TPD analysis certified the presence of HgS and elemental S on the surface of spent Ag/Fe-Ti spinel.