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[Display omitted] • Cyclic tests of CO 2 adsorption are performed at high temperature and pressure. • ETC is proposed as doing promoter with application under harsh sorption condition. • Excellent cyclic stability is achieved by MgO-ETC due to its porous structure. • LiNaK doping is found to lower the oxygen vacancy formation energy. • Deep K incorporation decreases oxygen ion migration energy from 3.68 to 2.04 eV. MgO-based sorbents are promising candidates for CO 2 capture as they are widely available and feasible in thermodynamics, but the development of MgO-based sorbents operating at elevated temperature and pressure is still a challenging task due to sintering. Herein, we selected eutectic carbonates with high melting point as promoters for the application under elevated conditions. Among various eutectic carbonates, MgO with eutectic ternary LiNaK carbonate (ETC) doping exhibited the highest MgO conversion thanks to crystal defects based on the XRD analysis. The highest CO 2 capture capacity of 0.73 g CO2 /g sorbent was obtained with 20 wt% ETC at 400 °C and 2 MPa. With further elevation of operating parameters to 540 °C and 5 MPa, the sample still shows a stable MgO conversion of 0.69 after 30 cycles, where the material exhibits a porous structure that inhibits the sintering. The density function theory calculations reveal that the LiNaK doping lowers the formation energy of surface oxygen vacancy, providing possibility for the subsequent oxygen ion migration. The deep K incorporation is most effective to promote the oxygen ion diffusion with decreased oxygen ion migration energy barrier from 3.68 to 2.04 eV. This study can guide the design of high-performance CO 2 sorbents at wider application conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Na 2 CO 3 addition can enhance the initial sorption rate of MgO-KNO 3 greatly. • CO 3 2– can improve sorption and diffusion rates by providing chemisorption sites. • A stable MgO conversion of 0.86 is achieved for MgO-Na 2 CO 3 -KNO 3 at 400 °C, 2 MPa. • MgO-Na 2 CO 3 -KNO 3 is feasible for actual precombustion CO 2 capture below 480 ℃,2 MPa. MgO-based sorbents are promising candidates for precombustion CO 2 capture performed at elevated temperature and pressure in thermodynamics, where the development of efficient sorbents is of great importance. Herein, we report MgO-Na 2 CO 3 -KNO 3 sorbents with fast sorption kinetics, high capture capacity and good cyclic stability at elevated conditions. The effects of nitrate species, Na 2 CO 3 doping amounts and sorption conditions on the MgO conversion were investigated during cyclic test. In comparison with LiNO 3 and NaNO 3 , the sample with KNO 3 possesses the highest MgO conversion, which increases from 0.78 to 0.86 after 30 cycles with sorption at 400 °C, 2 MPa. For nitrate-promoted MgO, Na 2 CO 3 plays an essential role in the initial fast sorption rate. The sorbent with 60 mol%Na 2 CO 3 possesses the highest MgO conversion of 0.89 after 30 cycles. Moreover, during the operation range of 400 ℃-480 ℃, 2 MPa, the sorbent exhibits an excellent cyclic stability with porous structure. Density functional theory calculations are further conducted to investigate the mechanism of performance improvement brought by Na 2 CO 3. We find dissolved CO 3 2– ions will provide chemisorption sites through the formation of C(CO 2)-O(CO 3 2–) bonds and can serve as the CO 2 carrier in molten nitrate salts, thus improving both sorption and diffusion rates of CO 2. [ABSTRACT FROM AUTHOR]

[Display omitted] • Li 3 PO 4 and CaCO 3 -doped, NaNO 3 -promoted MgO showed high CO 2 adsorption performance. • Li 3 PO 4 enhanced the surface adsorption of CO 2 by providing moderate basic sites. • CaCO 3 accelerated the carbonation of bulk MgO via the formation of CaMg(CO 3) 2. • The optimized sorbent showed good cyclic stability under harsh but realistic conditions. Molten nitrate-promoted MgO-based sorbents represent a potential class of materials for CO 2 capture at intermediate temperatures. However, their poor stability under harsh but realistic regeneration conditions (e.g., at high temperatures in pure CO 2) is a challenge for the application of CO 2 capture. In this work, a series of NaNO 3 and/or Li 3 PO 4 promoted MgO and MgO-CaCO 3 sorbents were prepared, characterized, and evaluated. The results showed that the NaNO 3 -Li 3 PO 4 promoted MgO-CaCO 3 sorbents had high CO 2 adsorption performance in terms of rate, capacity and stability, which was attributed to the promoting effect of Li 3 PO 4 and CaCO 3. Li 3 PO 4 can enhance the surface adsorption of CO 2 by providing some extra moderate basic sites, while CaCO 3 can accelerate the carbonation reaction of bulk MgO via the formation of CaMg(CO 3) 2. In addition, Li 3 PO 4 can hinder the sintering of sorbent particles, and consequently improve the stability of the sorbent. The optimized sorbent had a stable CO 2 uptake of 0.12 (or 0.26) g CO 2 /g sorbent when 30% (or pure) CO 2 was used at the adsorption stage in long-term cyclic operation (desorption at 500 °C in pure CO 2 for both cases), showing promising applications in intermediate-temperature CO 2 capture and thermochemical energy storage. [ABSTRACT FROM AUTHOR]