Revealing co-promotion mechanism of Mn/Ca3Al2O6 on CO2 adsorption performance of CaO in calcium looping by density functional theory

Calcium looping (CaL) is a promising technology for post-combustion CO2 capture and concentrated solar energy storage. The transition metal and calcium aluminate co-doped CaO materials have drawn a lot of attention due to the superior CO2 adsorption capacity. In this work, the co-promotion mechanism of Mn and Ca3Al2O6 on the CO2 adsorption of CaO-based materials in the calcium looping process was investigated by density functional theory. The structural properties and CO2 adsorption performance of CaO, Ca3Al2O6 doped CaO, and Mn/Ca3Al2O6 co-doped CaO structures were determined. The formation of O-Al and O-Mn bonds plays a crucial role in pre-venting the doped CaO from sintering. The adsorption energy of the CaO cluster on the Ca3Al2O6 and Mn/ Ca3Al2O6 surface is-5.66 and-11.15 eV, respectively, which is 2.4 and 4.7 times higher than that on the CaO surface, indicating the enhanced structural stability of the doped CaO. The presence of Ca3Al2O6 has less contribution to CO2 adsorption. The adsorption energy and charge transfer for CO2 on Ca3Al2O6-CaO (-2.03 eV,-0.73 e) is the same as pure CaO (-1.93 eV,-0.71 e). Introducing Mn remarkably improves CO2 adsorption performance by enhancing electron transport. The adsorption energy and charge transfer for CO2 on Mn/ Ca3Al2O6-CaO are the highest with-4.45 eV and-0.81 e, respectively. The Mn/Ca3Al2O6 co-doped CaO demonstrates superior structural stability and enhanced CO2 adsorption performance, which seems promising for efficient CO2 adsorption in the CaL process.