Interaction mechanism among CO, H 2 S and CuO oxygen carrier in chemical looping combustion: A density functional theory calculation study

When using coal-derived syngas or coal as fuel in chemical looping combustion (CLC), CO as a representative pyrolysis/gasification product and H 2 S as the main sulfurous gas coexist in fuel reactor. Either CO or H 2 S can absorb on the surface of CuO (the active component of Cu-based oxygen carriers), and reactions will occur among them. In this study, density functional theory (DFT) calculations are conducted to investigate the interaction among H 2 S, CO, and CuO, including: the reaction between CO and H 2 S over CuO particle, the influence of CO on the H 2 S dissociation and further reaction process, and the impact of H 2 S dissociation products on CO oxidation. Firstly, the co-adsorption results suggest that H 2 S might directly react with CO to produce COS via the Eley?Rideal mechanism, while CO prefers to react with HS * or S * via the Langmuir? Hinshelwood mechanism. This means that the reaction mechanisms between CO and H 2 S will change as the H 2 S dissociation proceeds, which has already been forecasted by the co-adsorption energies and verified by all of potential Eley?Rideal and Langmuir?Hinshelwood reaction pathways. Then, the influence of CO on the H 2 S dissociation process is examined, and it is noted that the presence of CO greatly limits the dissociation of H 2 S due to the increased energy barrier of the rate-determining dehydrogenation step. Furthermore, the impact of H 2 S dissociation products on CO oxidation by CuO is also investigated. The presence of H 2 S and S * significantly supresses the CO oxidation activity, while the presence of HS * slightly promotes the CO oxidation activity. Finally, the complete interaction mechanisms among H 2 S, CO, and CuO are concluded. It should be noted that COS will be inevitably produced via the Langmuir?Hinshelwood reaction between surface S * and CO *, which is prior to H 2 O generation and subsequent sulfidation reaction. ? 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.