Experimental and DFT studies of the role of H2S in Hg0 removal from syngas over CuMn2O4 sorbent

Abstract Elemental mercury (Hg0) and hydrogen sulfide (H2S) are two typical toxic pollutants in coal-derived syngas. The specific role of H2S in Hg0 elimination over CuMn2O4 sorbent and the involved reaction mechanism were systematically studied by experimental and theoretical methods. The synthesized CuMn2O4 sorbent was tested for Hg0 removal under simulated syngas and exhibited superior Hg0 capture performance (up to 95.6% at 200 °C). In the absence of H2S, both H2 and CO inhibited Hg0 removal over CuMn2O4, but the Hg0 removal efficiency was greatly improved after the introduction of 400 ppm H2S. H2S played a key role in Hg0 elimination in syngas by generating reactive sulfur species upon CuMn2O4. Density functional theory (DFT) calculations indicated that Hg0 and HgS were strongly chemisorbed upon CuMn2O4 surface with the adsorption energies of −129.84 and −220.21 kJ/mol, respectively. H2S was dissociatively adsorbed on CuMn2O4 and generated active sulfur species. Both H2S-pretreatment experiments and DFT calculations demonstrated that Hg0 reaction with H2S over CuMn2O4 occurred via a Langmuir–Hinshlwood mechanism, where chemisorbed Hg0 reacted with active sulfur species to form surface-bonded HgS. Furthermore, XPS and TPD analyses certified that the formation of active sulfur species and HgS upon the spent CuMn2O4 sorbents.