Roles for K2CO3 doping on elevated temperature CO2 adsorption of potassium promoted layered double oxides

Journal article

Despite the great attraction of using potassium promoted magnesium-aluminum layered double oxides (K-LDOs) as elevated temperature CO 2 adsorbents, the understanding of CO 2 adsorption mechanism of K-LDOs is still confusing and controversial due to the complexity of adsorbent compositions. In this work, in situ techniques were adopted to verify the synergistic mechanism of K 2 CO 3 doping (0–40 wt%) and Mg/Al mole ratio (0.55, 2.17, and 2.98) on the CO 2 capture of K-LDOs. Before K 2 CO 3 doping, the commercially available MG63 ([Mg 0.69 Al 0.31 (OH) 2 ](CO 3 ) 0.16 ·zH 2 O) exhibited the highest working CO 2 capacity of 0.320 mmol/g at 400 °C and 1 atm. After doping with 20 wt% K 2 CO 3 , K 20 -MG70 (Mg/Al ratio: 2.98) gave highest CO 2 capacity of 0.722 mmol/g. At low CO 2 partial pressures, however, K 20 -MG30 (Mg/Al ratio: 0.55) with the lowest Mg/Al ratio owned the best capture performance. Results from in situ Fourier transform infrared spectroscopy indicate that the changeable CO 2 adsorption performance of K-LDOs was controlled by two mechanisms. For K-LDOs with high Mg/Al ratios, the K 2 CO 3 doping is mainly localized in the bulk phase, and acts as a reactant to form high stable K-Mg double carbonates after adsorbing CO 2 . With increasing the Al content, surface modification occurs and becomes the dominant enhancement mechanism via the interaction between K + and unsaturated oxygen sites, which are generated by the partial substitution of Mg 2+ with Al 3+ . The reversible formation of bidentate carbonates are the main CO 2 species on K-Al 2 O 3 , K-LDOs, and K-MgO, whereas unidentate carbonates with a stronger binding affinity are only formed on K 20 -MG30, providing a superior performance for the adsorption of low concentration CO 2 .

Authors: Zhu, X; Chen, C; Wang, Q; Shi, Y; O'Hare, D

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Elsevier
• Journal: Chemical Engineering Journal
• Volume: 366
• Pages: 181-191
• Publication date: 2019-02-12
• Acceptance date: 2019-01-12
• DOI: 10.1016/j.cej.2019.01.192
• EISSN: 1873-3212
• ISSN: 1385-8947
• Keywords: In situ FTIR; FFR; adsorption mechanism; layered double oxides; elevated-temperature CO2 adsorption; potassium impregnation