Stabilization of NaNO₃-Promoted Magnesium Oxide for High-Temperature CO₂ Capture

Abstract

NaNO-promoted MgO sorbents are known to achieve enhanced CO sorption uptake but fail to maintain their capacity after multiple sorption-regeneration cycles. In this study, commercially available hydrotalcites (Pural Mg30, Pural Mg70, and synthetic hydrotalcite) were used as stabilizers for NaNO-impregnated MgO (MgONaNO) sorbents to improve their cyclic stability. Results show that the Mg30-stabilized MgONaNO attained higher and stable overall CO sorption performance as compared to bare MgONaNO after multiple sorption cycles. XRD analyses reveal that the hydrotalcites act as templates for MgCO by restricting the formation of large and nonuniform product crystallites. Furthermore, CO-TPD results show that the hydrotalcites cause a change in the basic sites of the sorbent, which may be attributed to its high interaction with both MgO and NaNO. This interaction becomes stronger as cycles proceed due to the structural rearrangements occurring, thus contributing to the stable behavior of the sorbents. However, these characteristics were not found on MgONaNO and the α-AlO-stabilized samples, thus proving the unique ability of hydrotalcites. From these results, we then derived the formation scheme of MgCO on the hydrotalcite-stabilized sorbents. This study presents a simple yet effective method of improving the stability of molten salt-promoted sorbents with promising potential for industrial use.

NaNO3‐Promoted Mesoporous MgO for High‐Capacity CO2 Capture from Simulated Flue Gas with Isothermal Regeneration

“…The different, advantageous behavior observed from the partially desorbed sample also led us to re‐examine the hypotheses about the nature of the rate limiting step in the CO 2 sorption using molten alkali‐metal‐promoted MgO sorbents. Until now, the two most supported suggestions regarding the rate limiting step in CO 2 sorption have been: 1) dissolution of MgO in the NaNO 3 medium to form [Mg 2+ ⋅⋅⋅O 2− ] ionic pairs or 2) formation of carbonate ions in the molten medium owing to the high solubility of O 2− ions in NaNO 3 medium . As previously observed in Figure S5, a significantly shortened induction period was observed for CO 2 sorption under exposure to pure CO 2 than under 10 % CO 2 /He.…”

“…Its potential as a promising candidate for CO 2 sorption grew even further following a report that porous MgO promoted by molten alkali metals enabled higher CO 2 sorption capacity and faster uptake kinetics in an intermediate temperature range (250–400 °C) than a bare MgO sorbent . As a result, there has been a growing interest in using such molten‐alkali‐metal‐promoted MgO for CO 2 capture in an intermediate temperature range . Zhang et al.…”

Effect of molten sodium nitrate on the decomposition pathways of hydrated magnesium hydroxycarbonate to magnesium oxide probed byin situtotal scattering

“…In recent years, a breakthrough in the development of effective MgO-based sorbents has been achieved through their promotion by molten salts. 9 The presence of molten alkali metal nitrates (such as LiNO 3 , NaNO 3 , KNO 3 and mixtures thereof ) drastically accelerates the rate of MgO carbonation; [10][11][12][13][14][15][16][17] however, an in-depth understanding of the role of molten salts in the carbonation of MgO has yet to be obtained. It has been proposed that molten salts act as a phase transfer catalyst in the reaction between MgO and CO 2 .…”

Structural and kinetic analysis of CO2 sorption on NaNO2-promoted MgO at moderate temperatures

“…Fortunately, doping alkali salts into MgO can significantly facilitate the sorption of CO 2 [20]. These alkali salts can be classified into four categories, i.e., single components [23][24][25][26][27], double salts [28][29][30][31], triple salts [32][33][34][35] and multiple salts [36,37]. For K 2 CO 3 -doped sorbents, recent studies indicate that the CO 2 sorption ability was increased to 10.2-11.7 wt% [38,39].…”