CO2 adsorption capacities measured for MMOs derived from LDHs

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

“Figure 11 shows the CO₂ adsorption capacities measured for MMOs derived from LDHs synthesized in the present study at 200°C and CO₂ partial pressure of 0.8 bar (80% v/v). The observed Mg/Al ratios and sodium content of the LDHs are also plotted in Figure 11 to investigate their relationship with the CO₂ adsorption capacities of derived MMOs. The error bars on the histogram represent the range of uncertainty due to the weighting precision of the thermogravimetric analyzer.”

“FIGURE 11. CO₂ adsorption capacities of MMOs synthesized via urea hydrolysis and co-precipitation methods at 200°C, plotted against the observed (measured) Mg/Al ratios and sodium content.”

“Figure 11 shows that the CO₂ adsorption capacities of MMOs obtained from the co-precipitation method (0.5–0.9 mmol/g) are generally higher than those obtained from the urea hydrolysis method (0.3–0.7 mmol/g). The higher observed Mg/Al ratios (i.e., Mg content), sodium content, and surface area of co-precipitated MMOs are likely the factors causing their CO₂ adsorption values to be higher than the urea hydrolysis derived MMOs. Among these parameters, the CO₂ adsorption capacities of co-precipitated MMOs seem more strongly influenced by their sodium content. For example, the highest CO₂ adsorption capacities were recorded from samples CPNI2 and CPCL3, which also presented the highest sodium content. No clear correlation between BET surface area (Figure 8) and CO₂ amount adsorbed is seen. From Figure 11, the Mg/Al ratio of the co-precipitated sorbents (both crystal and bulk Mg/Al ratios) does not seem to have an obvious impact on the CO₂ adsorption capacities; that is, the samples with different a-values and observed Mg/Al ratios (CPNI3, CPNI4, CPCL3, and CPCL4) showed close values of CO₂ adsorption capacities (0.75–0.81 mmol/g). Coincidentally, these samples also showed similar synthesis yield values (∼100%). Contrary to the synthesis method, different precursor salts do not play a major role in the CO₂ adsorption of MMOs. However, MMOs synthesized by metal nitrates show a slightly higher CO₂ adsorption capacity than those synthesized with metal chlorides in both synthesis methods. This is likely due to the higher sodium content in the precursor metal nitrates used to synthesize LDH samples.”