Influence mechanism of H2S on the reactivity of Ni-based oxygen carriers for chemical-looping combustion

• The adsorption mechanism of H2S on NiO(0 0 1) perfect and defect surface was investigated.
• The oxygen defect surface exhibits the high reactivity to the sequential dehydrogenation reaction of H2S.
• The influence mechanism of H2S on the CO adsorption and the diffusion of the O anion on NiO(0 0 1) surface is proposed.

First-principle calculations based on the density functional theory (DFT) were used to clarify the influence mechanism of H2S on the reactivity of Ni-based oxygen carriers. A systematic investigation about the adsorption behaviors of H2S on NiO(0 0 1) perfect and defect surface was firstly performed. H2S molecule is very likely to produce the sequential dehydrogenation reaction on NiO(0 0 1) defect surface, while this phenomenon was not observed on NiO(0 0 1) perfect surface. Then the mechanism of CO adsorption on the H2S pre-adsorption NiO(0 0 1) perfect and defect surface was clarified. It was revealed that the existence of H2S could notably restrain the CO adsorption process on NiO(0 0 1) surface. The H2S influence on the diffusion of the O anion in the NiO slab was also studied in detail. Results showed that the presence of H2S would lead to the higher thermodynamic driving force required for the O anion diffusion, limiting the rate of the diffusion.