Synthesis, characterization, and CO(2) adsorptive behavior of mesoporous AlOOH-supported layered hydroxides.

A novel CO(2) solid sorbent was prepared by synthesizing and modifying AlOOH-supported CaAl layered double hydroxides (CaAl LDHs), which were prepared by using mesoporous alumina (γ-Al(2)O(3)) and calcium chloride (CaCl(2)) in a hydrothermal urea reaction. The nanostructured CaAl LDHs with nanosized platelets (3-30 nm) formed and dispersed inside the crystalline framework of mesoporous AlOOH (boehmite). By calcination of AlOOH-supported LDHs at 700 °C, the mesoporous CaAl metal oxides exhibited ordered hexagonal mesoporous arrays or uniform nanotubes with a large surface area of 273 m(2) 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), Al(2)O(3), and CaAlO mixed oxides. The mesoporous metal oxides were used as a solid sorbent for CO(2) adsorption at high temperatures and displayed a maximum CO(2) capture capacity (≈45 wt %) of the sorbent at 650 °C. Furthermore, it was demonstrated that the mesoporous CaAl oxides showed a more rapid adsorption rate (for 1-2 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 CO(2) at high temperature.