Double-exchange-induced effective increased CO2 capture of CaO by doping bimetallic oxides with variable valence state
Motivated by the double exchange interaction between the adjacent magnetic ions in the magnetic oxides would lead to the generation of more oxygen vacancy to improve the CO 2 capture of CaO, here we report a double-exchange-induced effective increase of CO 2 performance of calcium-based adsorbent by incorporating bimetallic oxides with variable valence state (i.e. Fe, Mn, Ce, Cu) into CaO. The (Fe-Mn)-doped CaO sample exhibits excellent CO 2 adsorption capacity and carbonation conversion, remaining stable at 0.61 g CO 2 /g adsorbent and 95% after 20 cycles, respectively. The enhanced performance are attributed to uniform distribution of Fe 2 O 3 and Ca 2 MnO 4 particles preventing CaO crystallite growth and agglomeration. The (Fe-Mn)-doped sample with much thinner flake structure and the largest pore diameter is loose and porous, thus favoring CO 2 diffusion inside the particles and preventing sintering during carbonation period. The electron transfer between Fe and Mn carried out by the famous double exchange may boost the generation of oxygen vacancy and the effective improvement of the CO 2 affinity for the calcium-based adsorbent, which are significant to the diffusion of CO 3 2– and mobility of O 2– according to the mechanism of CO 2 adsorption. In addition, the (Fe-Mn)-doped adsorbent exhibits the fastest adsorption kinetics, and the synergistic interaction of Fe and Mn can significantly reduce the activation energy of carbonation reaction. The famous double-exchange interaction of magnetic metal oxide can occur by intermediate oxygen p orbits between adjacent Fe and Mn metal ions with different d orbital occupancies in the (Fe-Mn)-modified calcium-based adsorbent, which provides a unique way to design CO 2 adsorbent.
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