Abstract
Improving the cyclic CO(2) uptake stability of CaO-based solid sorbents can provide a means to lower CO(2) capture costs. Here, we develop nanostructured yolk(CaO)-shell(ZrO(2)) sorbents with a high cyclic CO(2) uptake stability which outperform benchmark CaO nanoparticles after 20 cycles (0.17 g(CO(2)) g(Sorbent)(-1)) by more than 250% (0.61 g(CO(2)) g(Sorbent)(-1)), even under harsh calcination conditions (i.e. 80 vol% CO(2) at 900 °C). By comparing the yolk-shell sorbents to core-shell sorbents, i.e. structures with an intimate contact between the stabilizing phase and CaO, we are able to identify the main mechanisms behind the stabilization of the CO(2) uptake. While a yolk-shell architecture stabilizes the morphology of single CaO nanoparticles over repeated cycling and minimizes the contact between the yolk and shell materials, core-shell architectures lead to the formation of a thick CaZrO(3)-shell around CaO particles, which limits CO(2) transport to unreacted CaO. Hence, yolk-shell architectures effectively delay CaZrO(3) formation which in turn increases the theoretically possible CO(2) uptake since CaZrO(3) is CO(2)-capture-inert. In addition, we observe that yolk-shell architectures also improved the carbonation kinetics in both the kinetic- and diffusion-controlled regimes leading to a significantly higher cyclic CO(2) uptake for yolk-shell-type sorbents.