Exploring the microscopic reaction mechanism of H2S and COS with CuO oxygen carrier in chemical looping combustion

Abstract

Density functional theory (DFT) calculations are employed to investigate the reaction mechanisms of H2S or COS with CuO in this work, including the microscopic adsorption, dissociation, and further reactions over the perfect (fresh) and defect (partially reduced) CuO (111) surfaces. On the perfect surface, the elementary reaction of HS* → H* + S* is the rate-determining step in the two-step H2S dissociation process, and the formation of H2O is however the rate-determining step for the whole reaction between H2S and CuO. As for the defect surface, the reaction of H2O formation is still a more preferable pathway than the complete dissociation and H2 formation route. In view of COS decomposition on the perfect surface, the energy barriers for the formation of CO or CO2 from COS decomposition are too high, and thus are difficult to take place. On the defect surface, the presence of oxygen vacancy greatly promotes the adsorption and subsequent decomposition of COS. Finally, the remaining sulfur favorably exists on the surface rather than SO2 formation, and copper sulfides will inevitably generate as the dissociations of H2S or COS proceed. The results attained in this work are helpful to give insights into the sulfur evolution of sulfur-containing fuels in the chemical looping combustion process.