Synthesis and Evaluation of K-Promoted Co_3-xMg_xAl-Oxides as Solid CO₂ Sorbents in the Sorption-Enhanced Water−Gas Shift (SEWGS) Reaction

Hydrogen is essential in a variety of large-scale chemical processes. As a carbon-free energy carrier, hydrogen has a potential for wide use within power production and transportation. However, most of the recent production methods involve the release of CO₂ as a by-product. Hence, decarbonization of hydrogen production is one step to reduce CO₂ emission into the Earth’s atmosphere. Several process schemes have been suggested for low-carbon emission production of hydrogen. In this work, we show how to improve solid sorbents for the sorption-enhanced water–gas shift (SEWGS) process, which is a process that exploits a solid sorbent in the water–gas shift reactor to capture CO₂ in situ and drive the process toward an improved hydrogen yield. We report herein a series of Co_xMg_3‑xAl materials based on hydrotalcites, promoted with various loadings of K. The materials have been characterized by BET, XRD, and NMR and tested for their CO₂ adsorption performance in three adsorption–desorption cycles in a lab-scale fixed-bed reactor (20–22 bar, CO₂ + steam as reactant gas, and isothermal conditions at 375 and 400 °C). The most promising material was subjected to a long-term test (120 adsorption–desorption cycles at similar conditions). This test indicates that a K-promoted Co_1.5Mg_1.5Al (22 wt % of added K₂CO₂ to the oxide) material has a higher cyclic capacity for CO₂ than standard reference cases. We have estimated that the volumetric capacity (in mol/L unit) of this sorbent will be 23–26% higher than a standard reference material at 400 °C and 30–39% higher at 375 °C. This would, in fixed-bed columns, lead to significant reduction in the needed column volumes in the final process and reduce costs.