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

Elemental mercury (Hg-0) and hydrogen sulfide (H2S) are two typical toxic pollutants in coal-derived syngas. The specific role of H2S in Hg-0 elimination over CuMn2O4 sorbent and the involved reaction mechanism were systematically studied by experimental and theoretical methods. The synthesized CuMn2O4 sorbent was tested for Hg-0 removal under simulated syngas and exhibited superior Hg-0 capture performance (up to 95.6% at 200 degrees C). In the absence of H2S, both H-2 and CO inhibited Hg-0 removal over CuMn2O4, but the Hg-0 removal efficiency was greatly improved after the introduction of 400 ppm H2S. H2S played a key role in Hg-0 elimination in syngas by generating reactive sulfur species upon CuMn2O4. Density functional theory (DFT) calculations indicated that Hg-0 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 Hg-0 reaction with H2S over CuMn2O4 occurred via a Langmuir-Hinshlwood mechanism, where chemisorbed Hg-0 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.