Improved hydrogen production via sorption-enhanced ethanol steam reforming: Influence of the Mg:Al molar ratio in K-promoted MgAl layered double oxides as CO2 sorbents

Abstract

In this study, the influence of the Mg:Al molar ratio on the performance of K-promoted layered double oxide CO2 sorbents, specifically designed for hydrogen production via sorption-enhanced ethanol steam reforming (SE-ESR) was considered. The synthesis of hydrotalcite precursors with varying Mg:Al ratios was performed to assess how this parameter affects the physicochemical properties of the resulting K-promoted layered double oxides (KLDO), including their morphology, structure, basic character, and how these characteristics relate to the CO2 sorption capacity. The sample with a Mg:Al ratio of 4:1, showed the best performance, both in terms of CO2 sorption capacity under dry conditions and of H2 purity under SE-ESR at 500 ◦C, with H2 purities close to 100 % and yields around 5.5 mol of H2 per mol of ethanol fed to the reactor during the first cycle of SE-ESR. This behavior was attributed to its high concentration of basic sites, in particular, strong basic sites. Furthermore, the stability of the most effective sorbent was tested over 20 SE-ESR - regeneration cycles, demonstrating its potential for long-term operation to produce high-purity H2, with purities higher than 90 % throughout all cycles and CO contents lower than 5 %. The results obtained demonstrated the potential of this intensified process, reaction and simultaneous CO2 capture, allowing the production of high-purity H2, reducing investment costs and improving energy efficiency.