Interaction mechanism between CO and H2S over CuFe2O4 oxygen carrier during chemical-looping combustion: A DFT study

During the chemical-looping combustion process, CO as an important part of syngas and H2S as a common sulfur compound inevitably coexist in the fuel. Based on the density functional theory and periodic structure model, the interaction mechanism between CO and H2S over the O-defective CuFe2O4 surface was comprehensively investigated. The results show that the adsorption energies of adsorbates on the O-defective surface are in the order of S* (-205.42 kJ/mol) > HS* (-191.37 kJ/mol) > CO (-44.88 kJ/mol) > H2S* (-28.97 kJ/mol). CO adsorption over the O-defective surface is dominant as compared to H2S adsorption. The adsorption energies of CO in the presence of H2S, HS* and S* are -73.21, -255.98 and -105.35 kJ/mol, respectively. The adsorption strength of CO over the O-defective surface was enhanced in the presence of HS* or S*. The presence of CO* will greatly limit the H2S dehydrogenation process, especially for the second dehydrogenation step. The energy barriers of CO oxidation with the participation of H2S*, HS* and S* are 69.66, 51.42 and 14.19 kJ/mol, respectively. COS may be produced form the reaction between CO and S* with an energy barrier of 27.13 kJ/mol, following the Eley-Rideal reaction mechanism. CuFe2O4 oxygen carrier exhibits good anti-sulfur ability because the reaction of CuFe2O4 with CO and H2S kinetically prefers the CO oxidation pathway rather than the COS formation pathway.