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• The adsorption of CO 2 and H 2 O by CaO/Ca 12 Al 14 O 33 was studied by DFT calculations. • The chemical adsorption of CO 2 and H 2 O on Ca 12 Al 14 O 33 -supported CaO is competitive. • The adsorption of CO 2 on Ca 12 Al 14 O 33 -supported CaO is stronger than that of H 2 O. • The adsorbed H 2 O activates adjacent O atoms of CaO, which benefits CO 2 adsorption. • The DFT can predict the CO 2 adsorption performance of different CaO-based sorbents. The synthetic CaO/Ca 12 Al 14 O 33 sorbent has been regarded as an efficient CO 2 sorbent during the calcium looping cycles. In this work, the CO 2 adsorption performance of the synthetic CaO/Ca 12 Al 14 O 33 sorbent in the presence of H 2 O was investigated by density functional theory (DFT) calculations. DFT was used to analyze the adsorption of CO 2 and H 2 O on the synthetic sorbent. Both structural parameters (atomic layout and electronic configuration) and the adsorption parameters (energy, bond lengths, angles, bond population and charge transfer) of CO 2 and H 2 O on the synthetic sorbent were determined. To confirm the feasibility of DFT analysis, the CO 2 capture performance of the synthetic sorbent in the presence of steam was examined in a dual fixed bed reactor. The results indicate strong interactions between the C atom and the O atom in CaO and interactions between the H atom and the O atom in CaO. The higher adsorption energy of CO 2 than H 2 O on pristine CaO and Ca 12 Al 14 O 33 -supported CaO suggests that the adsorptions of CO 2 and H 2 O are competitive and that the adsorption of CO 2 is stronger than that of H 2 O. The adsorption of H 2 O leads to the activation of adjacent O atoms of CaO and thus stronger CO 2 adsorption on the O atom with H 2 O adsorbed. The electrons in the p orbital of the O atom near the Fermi level play important roles in CO 2 adsorption by CaO. The presence of Ca 12 Al 14 O 33 hinders CO 2 adsorption by CaO. A low Ca 12 Al 14 O 33 content in synthetic sorbents should be maintained to ensure high CO 2 capture capacity and sintering resistance of synthetic sorbents. DFT calculations can predict the CO 2 adsorption performance of CaO-based sorbents with additives under different reaction atmospheres. [ABSTRACT FROM AUTHOR]

Highlights • Synthetic CaO-based CO 2 sorbent was prepared using paper fibre as a biotemplate. • Synthetic sorbent is mainly composed of CaO and Ca 12 Al 14 O 33. • Synthetic sorbents possess microtube-like structure with superior CO 2 uptake. • Synthetic sorbent has improved sintering resistance in severe calcination condition. Abstract Calcium looping is regarded as an effective and viable way to address CO 2 emissions. To overcome the loss-in-capacity problems of calcium-based sorbents with the number of calcium looping cycles, a novel CaO/Ca 12 Al 14 O 33 sorbent with a microtube-like structure was prepared from carbide slag and Al(NO 3) 3 ·9H 2 O using paper fibre as a biotemplate. The CO 2 capture performance and microstructure of the novel synthetic sorbent under calcium looping conditions were investigated. The results show that the utilization of the biotemplate is good to retain the high cyclic CO 2 capture reactivity of the synthetic sorbent. Due to the unique hollow porous structure, the CO 2 capture capacity of the synthetic sorbent containing 7.5 wt% Al 2 O 3 retains 0.56 and 0.33 g/g after 30 cycles under mild and severe calcination conditions, respectively, which are 2.56 and 2.11 times higher than those of carbide slag under the same respective calcination conditions. With the presence of 10% steam in the carbonation atmosphere, the CO 2 capture capacity of the synthetic sorbent retains 0.55 g/g under the severe calcination conditions after 10 cycles. The native hierarchical biostructure of paper fibre is preserved in the synthetic sorbent. CaO and Ca 12 Al 14 O 33 are uniformly distributed in the synthetic sorbent, resulting in a high sintering resistance during multiple CO 2 capture cycles. CO 2 can penetrate through the microtube-like structure of the synthetic sorbent from two directions, i.e., from the outer surface and inner surface. This phenomenon effectively enlarges the contact area between CO 2 and CaO. The CaO/Ca 12 Al 14 O 33 sorbent with a hollow porous structure by means of a biotemplate appears promising in the calcium looping technology for CO 2 capture. [ABSTRACT FROM AUTHOR]

• Novel SiC/Mn co-doped CaO pellets are prepared for calcium looping heat storage. • Co-doped pellets show good heat storage capacity in multiple heat storage cycles. • Optical and thermal capacities of pellets rise by 16.6 and 2.2 times, respectively. • Co-doped pellets exhibit high crushing strength and attrition resistance in cycles. To achieve high heat storage capacity, excellent mechanical, optical and thermal properties in calcium looping thermochemical heat storage, the novel SiC/Mn co-doped CaO pellets were fabricated by the extrusion-spheronization method. The heat storage performances of the novel CaO pellets were studied under harsh calcination (pure CO 2 , 950 °C) and pressurized carbonation (pure CO 2 , 13 bar, 800 °C) conditions in a dual fixed-bed reactor system. The additions of SiC and Mn enhance the cyclic stability of CaO pellets during the multiple heat storage cycles. When the mass ratio of CaO:SiC:MnO 2 is 100:5:5, the co-doped CaO pellets exhibit an excellent heat storage performance. The effective conversion and heat storage density of the co-doped CaO pellets are 41.5% higher than those of original CaO pellets, respectively. Meanwhile, the co-doped CaO pellets possess a good optical absorption capacity and a high thermal conductivity, which are 17.6 and 3.2 times as high as those of original CaO pellets, respectively. In addition, the co-doped CaO pellets show much higher crushing strength and lower weight loss during the attrition test. The stronger interaction between SiC and CaO cluster mitigates the movement of CaO, which is determined by density functional theory simulation. The adsorption of CO 2 onto the CaO surface is enhanced by the addition of Mn. Therefore, SiC/Mn co-doped CaO pellets used in the calcium looping thermochemical heat storage process appear promising. [ABSTRACT FROM AUTHOR]