Revealing the Role of MgO in Sorption-Enhanced Water Gas Shift Reaction for H2 Production: A DFT Study

The sorption-enhanced water gas shift (SEWGS) process has emerged as a promising technology for high-purity H-2 production. MgO serves as a competitive sorbent in SEWGS, removing CO2 in situ. Yet the reaction mechanism of SEWGS employing MgO is not well understood. In this work, the reaction mechanism of SEWGS on the MgO surface is revealed by density functional theory (DFT) analysis. The MgO(110) surface shows a remarkable enhancement for SEWGS. Spontaneous dissociation of H2O is observed whether in the presence of CO or CO2, leading to the enrichment of hydroxyl groups for subsequent reactions. CO2 generated is captured by surface basic sites, resulting in the formation of MgCO3. The presence of the generated hydroxyl group enhances the dehydrogenation reaction on the surface, facilitating hydrogen production. The reaction pathway is described as follows. First, spontaneous dissociation of H2O occurs when co-adsorbed with CO on the MgO surface. Then, two hydroxyl groups interact, yielding atomic O for CO oxidization and atomic H for H-2 generation. Ultimately, CO2 is captured by the surface while H-2 desorbs from the surface. The rate-limiting step is H-2 generation with an energy barrier of 0.68 eV. The calculation results elucidate the enhancement mechanism of MgO on the SEWGS process.