CO2 Sorption Durability of Zr-Modified Nano-CaO Sorbents with Cage-like Hollow Sphere Structure

Novel Zr-modified nano-CaO sorbents with cage-like hollow sphere structure were prepared for increasing the durability of CO2 sorption via an ion precipitation method using carbon spheres as a template. A thorough study on the influence of the Ca/Zr molar ratio and the effect of cage-like structure on the CO2 sorption durability of the prepared sorbents was performed using thermogravimetric analysis. It was found that the optimum Ca/Zr molar ratio of 5 maintained the most favorable CO2 sorption stability, which maintained a CaO conversion of 76% after 30 cycles, whereas the CaO conversion of a nano-CaO cage-like hollow sphere sorbent without Zr-modification decayed to 20%. The combination of the Zr-modification and the cage-like structure demonstrates a synergistic effect in enhancing the CaO conversion and sorption stability due to the formation of CaZrO3 with a cage like porous structure, which facilitated CO2 diffusion and minimized thermal sintering. Furthermore, a detailed comparison was made among the Zr-, Mg- and Al-stabilizers. It was found that the Zr-stabilized sorbents exhibited better durability than that of Al- and Mg-stabilized sorbents due to the formation of CaZrO3 with a high Tammann temperature (T-T).