Enhanced CO2 adsorption of MgO with alkali metal nitrates and carbonates

Abstract

Carbon capture and storage is an effective way to mitigate the accumulation of greenhouse gases in the atmosphere. In this work, a series of MgO-basedadsorbents were synthesized by deposition of a mixed alkali metal nitrates and carbonates. The CO₂ capture amount of the compound adsorbent is enlarged as 19.06 mmol·g⁻¹ at 325 °C when loading 10% mole of [(Li_0.44K_0.56)NO₃]₂[(Na_0.5K_0.5)CO₃]. The as-synthesized adsorbent also exhibits stable CO₂ capture performance after long-term adsorption/desorption cycles. The effects of the molar ratio of alkali metal salts and adsorption conditions were investigated. The adsorption enhancement mechanism is discussed regarding the changes of composite microstructure during the reaction. It is found that the CO₂ uptake curve has three adsorption stages corresponding to the interactions between CO₂, MgO/metal nitrates and carbonates. The nitrite product plays a key role in the improvement of CO₂ uptake since it not only yields more O²⁻ but also reacts with MgO in molten nitrites to produce an intermediate nitrato compound, which leads to the rapid nucleation of MgCO₃ by triggering lattice defects. It is found that the CO₂ uptake decreased from 19.06 to 15.7 mmol·g⁻¹ over 30 cycles, which proves that the new adsorbents have a good long-term adsorption/desorption stability.