title: CO₂ sorbents with scaffold-like Ca-Al layered double hydroxides as precursors for CO₂ capture at high temperatures.
abstract: A highly stable high-temperature CO₂ sorbent consisting of scaffold-like Ca-rich oxides (Ca-Al-O) with rapid absorption kinetics and a high capacity is described. The Ca-rich oxides were prepared by annealing Ca-Al-NO₃ layered double hydroxide (LDH) precursors through a sol-gel process with Al(O(i)P)₃ and Ca(NO₃)₂ with Ca(2+)/Al(3+) ratios of 1:1, 2:1, 4:1, and 7:1. XRD indicated that only LDH powders were formed for Ca(2+)/Al(3+) ratios of 2:1. However, both LDH and Ca(OH)₂ phases were produced at higher ratios. Both TEM and SEM observations indicated that the Ca-Al-NO₃ LDHs displayed a scaffold-like porous structure morphology rather than platelet-like particles. Upon annealing at 600 °C, a highly stable porous network structure of the CaO-based Ca-Al-O mixed oxide (CAMO), composed of CaO and Ca₁₂Al₁₄O₃₃, was still present. The CAMO exhibited high specific surface areas (up to 191 m(2)g(-1)) and a pore size distribution of 3-6 nm, which allowed rapid diffusion of CO₂ into the interior of the material, inducing fast carbonation/calcination and enhancing the sintering-resistant nature over multiple carbonation/calcination cycles for CO₂ absorption at 700 °C. Thermogravimetric analysis results indicated that a CO₂ capture capacity of approximately 49 wt% could be obtained with rapid absorption from the porous 7:1 CAMO sorbents by carbonation at 700 °C for 5 min. Also, 94-98% of the initial CO₂ capture capability was retained after 50 cycles of multiple carbonation/calcination tests. Therefore, the CAMO framework is a good isolator for preventing the aggregation of CaO particles, and it is suitable for long-term cyclic operation in high-temperature environments.
authors: Department of Materials Science and Engineering, National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu Taiwan 300, ROC.
authors: Po-Hsueh
authors: PH
authors: Chang
authors: Tai-Jung
authors: TJ
authors: Lee
authors: Yen-Po
authors: YP
authors: Chang
authors: San-Yuan
authors: SY
authors: Chen
mesh_terms: D000042:Absorption; D000535:Aluminum / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry*; D002245:Carbon Dioxide / Q000737:chemistry* / Q000302:isolation & purification*; D006878:Hydroxides / Q000737:chemistry*; D007700:Kinetics; D008958:Models, Molecular; D008968:Molecular Conformation; D013696:Temperature
chemical_list: D006878:Hydroxides; D002245:Carbon Dioxide; D000535:Aluminum; D002118:Calcium