MgO-based CO₂ Sorbents Promoted By Alkali Metal Salts:Preparation And Structure-Performance Relationship

Effective CO₂ capture has attracted much attention in recent years because of global warming and climate change concerns,and one of the hot issues is sorbent materials suitable for CO₂ capture.The main objective of this thesis is to develop a facile method for preparing high-performance MgO-based CO₂ sorbents and explore the structure-performance relation-ship.First,a series of MgO-based sorbents promoted by alkali metal nitrate and carbonate were prepared by a simple precipitation-deposition method.The structural properties of MgO-based sorbents were tuned by varying the alkali metal salts,the molar ratio of nitrate to carbonate,and the molar ratio of total salts to MgO,and characterized by various techniques,including N2 physisorption,XRD,DSC,FESEM and HRTEM.In addition,the CO₂ capture performance of the sorbent was evaluated using a thermogravimetric analyzer.The results showed that the sorbents promoted by both alkali metal nitrate and carbonate exhibited high C02 uptake and in particular,the sobent with a nitrate/carbonate molar ratio of 2 and a total salts/MgO molar ratio of 0.15 possessed the best CO₂ capture performance,whose CO₂ uptake remained constant after 20 sorption-regeneration cycles under a low CO₂ concentration of 40%,being around 0.52 gCO₂/g_sorbent.In addition,the CO₂ uptake of the MgO-based sorbent was found to have no direct relationship with the specific surface area of sorbent,because even though the surface area of sorbent was close to zero,the conversion of MgO still reached 80%.Based on the experimental results,a reasonable CO₂ sorption mechanism was proposed for the alkali metal salt-promoted MgO-based sorbent,which can describe the C02 sorption behavior very well.Next,a novel solvothermal-deposition method was developed to prepare alkali metal salt-promoted MgO-based sorbents,whose micromorphologies were adjusted by using different surfactants.The structural properties of sorbents were characterized and the CO₂ capture performance was evaluated and compared.It was found that flower-like MgO nano-particles were prepared using polyvinylpyrrolidone as the surfactant,and after coating of alkali metal salts with optimal composition on the surface of MgO,the resulting MgO-based sorbent displayed excellent C02 capture performance,whose CO₂ uptake was as high as 0.68 gCO₂/g_sorbent during 20 cycles and without any obvious decrease.