CaO-based CO₂ sorbents for direct solar-driven calcium looping synthesized by impregnated layer solution combustion method

Calcium looping （CaL） CO₂ capture technology exhibits broad application prospects due to the advantages of CaO sorbents, such as high theoretical adsorption capacity, low raw material cost, and wide availability. However, the traditional coal-blended combustion calcination method adopted in CaL systems tends to cause interactive reactions between coal-derived impurity components and active CaO, leading to the deactivation of CaO-based sorbents. Replacing coal-blended combustion with concentrated solar direct calcination can effectively avoid the negative impacts of coal-derived impurities on CaO-based sorbents, but sorbents in this mode need to simultaneously possess excellent CO₂ cyclic adsorption stability and superior spectral absorption characteristics. In this study, Mn-supported CaO-based sorbents were prepared via the impregnated template-assisted combustion synthesis method. The effects of combustion synthesis temperature, types of impregnated templates, and Mn loading ratio on the CO₂ cyclic adsorption performance of the sorbents were systematically investigated. The results show that when degreased cotton is used as the impregnated template, the prepared sorbent achieves a maximum CO₂ capture capacity of 0.380 g/g after 17 cycles due to the improved pore structure. The combustion synthesis temperature has a significant influence on the CO₂ capture performance of the sorbents. The CaO-based sorbent prepared at 750 ℃ exhibits a loose and porous structure, which can effectively prevent excessive sintering of the sorbent and inhibit the in-situ formation of CaCO₃ phase. Thus, 750 ℃ is determined as the optimal combustion synthesis and calcination temperature. In the Mn-supported CaO-based sorbents, Ca₂MnO₄ grains are uniformly distributed, which significantly suppresses the sintering effect of the sorbents during high-temperature cycles and thereby enhances their adsorption performance. Among them, the CaO-based sorbent with a 15% Mn loading ratio shows excellent CO₂ cyclic adsorption performance and a high average solar spectral absorptivity （~41%）. Comprehensive analysis indicates that the 15% Mn-supported CaO-based sorbent directly synthesized via combustion at 750 ℃ using degreased cotton as the impregnated template is a potential high-performance sorbent for CaL carbon capture systems.