Adsorption mechanisms of sulfur-containing radicals on different copper oxide surfaces investigated by the first-principles combined with experiments during coal pyrolysis

In this study, Erdos (ED) high sulfur coal was selected to investigate the sulfur fixation effect of copper oxide (CuO) on H₂S, SO₂, COS and sulfur-containing radicals formed during pyrolysis by the gas chromatography (Py-GC) and XPS combined with density functional theory (DFT) calculations. By Py-GC analysis, H₂S, COS and SO₂ release of ED coal significantly decrease after adding 6% CuO, illustrating CuO can adsorb sulfur-containing radicals and prohibit the generation of these three sulfur-containing gases. The adsorption mechanisms of sulfur-containing radicals produced during coal pyrolysis on different CuO surfaces were investigated by DFT calculations. After optimization, the multi-adsorption configurations of ·S·, ·SH and ·S–S· on different CuO (111, O-terminated 110 and Cu-terminated 110) surfaces can be obtained. According to their highest absolute adsorption energies, the O-terminated CuO (110) surface is more favorable for ·S· and ·SH adsorption rather than other two surfaces, while the Cu-terminated CuO (110) surface for the adsorption of ·S–S· and the co-adsorption of ·S·, ·SH and ·S–S· during coal pyrolysis. Furthermore, ·SH is easily dissociated on the O-terminated CuO (110) surface. The S atoms of ·S· and ·SH are bonded with two Cu_suf atoms, and every S atom of ·S–S· combines with one Cu_suf on the Cu-terminated CuO (110) surface, leading to the generation of two substances similar to Cu₂S and sulfide during co-adsorption. This is very consistent with the apparent appearing peak of Cu₂S and remaining peak of sulfide in XPS spectra of CuO-ED char. Thus, these DFT theoretical calculations can testify the experimental results of CuO inhibiting H₂S, COS and SO₂ to release.