Synthesis, Characterization, and CO2 Adsorptive Behavior of Mesoporous AlOOH-Supported Layered Hydroxides

A novel CO2 solid sorbent was prepared by synthesizing and modifying AlOOH-supported CaAl layered double hydroxides (CaAl LDHs), which were prepared by using mesoporous alumina (?-Al2O3) and calcium chloride (CaCl2) in a hydrothermal urea reaction. The nanostructured CaAl LDHs with nanosized platelets (330 nm) formed and dispersed inside the crystalline framework of mesoporous AlOOH (boehmite). By calcination of AlOOH-supported LDHs at 700 degrees C, the mesoporous CaAl metal oxides exhibited ordered hexagonal mesoporous arrays or uniform nanotubes with a large surface area of 273 m2?g-1, a narrow pore size distribution of 6.2 nm, and highly crystalline frameworks. The crystal structure of the calcined mesoporous CaAl metal oxides was multiphasic, consisting of CaO/Ca(OH)2, Al2O3, and CaAlO mixed oxides. The mesoporous metal oxides were used as a solid sorbent for CO2 adsorption at high temperatures and displayed a maximum CO2 capture capacity (approximate to 45 wt?%) of the sorbent at 650 degrees C. Furthermore, it was demonstrated that the mesoporous CaAl oxides showed a more rapid adsorption rate (for 12 min) and longer cycle life (weight change retention: 80?% for 30 cycles) of the sorbent because of the greater surface area and increased number of activated sites in the mesostructures. A simple model for the formation mechanism of mesoporous metal oxides is tentatively proposed to account for the synergetic effect of CaAl LDHs on the adsorption of CO2 at high temperature.