Ag doping Fe-Ti spinel sorbent for Hg0 removal from syngas and the mechanism investigation

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 (Hg0) from syngas at high temperatures (200-350 degrees C). The role of H2S on Hg0 elimination over Ag/Fe-Ti spinel and the Hg0 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 Hg0 removal from the simulated syngas and showed an average mercury removal efficiency above 90 % at 250 degrees C. Loading Ag effectively enhanced Hg0 removal activity in high -temperature syngas by generating Ag-Hg alloy via the amalgamation reaction. H2S played the most important role in mercury removal, by adsorbing Hg0 on Ag/Fe-Ti spinel sorbent surface to form active sulfur species. H2S-pretreatment experiments indicated that the reaction of H2S and Hg0 occurred via the Langmuir-Hinshelwood mechanism. Stability and cyclic regeneration experiments indicated that the Ag/Fe-Ti spinel had good regen-eration performance and reusability. Density functional theory (DFT) calculation was performed to elucidate that strong chemisorption for H2S 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 Hg0 removal mechanism, which the chemisorbed Hg0 reacted with active sulfur species to generated surface-bound HgS. Both XPS and Hg0-TPD analysis certified the presence of HgS and elemental S on the surface of spent Ag/Fe-Ti spinel.

Automated summary

A series of Ag doping Fe-Ti spinel sorbents were synthesized and employed to remove elemental mercury from syngas. H2S played a crucial role in the Hg0 elimination process, by adsorbing Hg0 on the sorbent surface to form active sulfur species. Experimental and theoretical methods were used to systematically investigate the Hg0 removal mechanism.