Stability of CO2 adsorption using MMOs derived from LDHs

https://doi.org/10.3389/fenrg.2022.882182

“Cyclic CO₂ adsorption tests were carried out to test the cyclic stability of selected LDH-derived MMOs sorbents and compared with pure magnesium oxide (MgO, obtained by calcining Mg(OH)₂ at 400°C for 4 h), which serves as the reference case. MgO is a suitable benchmark to assess the cyclic stability of LDH-derived MMOs because the MMOs sorbents were originally proposed as an alternative option to MgO, which was found to have poor cyclic stability in general. Only four MMOs were selected to study for cyclic tests based on three criteria: 1) highest LDH yields, 2) good agreement between expected and observed Mg/Al ratios, and 3) adequate CO₂ adsorption capacities. Note that the adsorption and desorption were carried out for 30 min each. Figure 13 shows the CO₂ adsorption capacities of tested MMOs sorbents in each cycle and the percentage reduction in CO₂ sorption capacities calculated with respect to the amount adsorbed in the first cycle.”

“FIGURE 13. (A) CO₂ adsorption capacity and (B) percentage reduction in adsorption capacity by cycles of selected MMOs synthesized with the urea hydrolysis and co-precipitation methods.”

“Figure 13A shows that all LDH-derived MMOs and MgO sorbents show a slow gradual drop in CO₂ adsorption capacities over 10 adsorption cycles and there is no obvious plateau, which means the capacities might reduce further. A similar trend is observed in Figure 13B, which shows the percentage drop of adsorption capacities calculated with respect to the first cycle. It seems that all the sorbents experience the largest drop in the adsorption capacities after the first cycle. No obvious correlation from either the synthesis method or metal salts precursors affects this large initial drop in adsorption capacities. Among the MMO samples, Figure 13A shows that CPNI3 sample presents the highest CO₂ adsorption capacities in all 10 cycles. Interestingly, despite the promising outlook of CPNI3, a close look in Figure 13B can find that, in fact, the same sorbent shows the largest reduction in overall cyclic stability (31.2%) and is the only MMOs sorbent performing worse than MgO sorbent (26.5%). On the contrary, the urea hydrolysis samples show relative good cyclic performance than their co-precipitated counterparts, as their CO₂ adsorption capacities after the first cycles are almost similar in Figure 13A. Overall, LDH-based MMOs appear to have better cyclic stability than pure MgO sorbent (i.e., lower percentage loss in CO₂ adsorption capacities after the first cycle).”