Abstract
Solid sorbents are essential for developing technologies that directly capture CO(2) from air. In solid sorbents, metal oxides and/or alkali metal carbonates such as potassium carbonate (K(2)CO(3)) are promising active components owing to their high thermal stability, low cost, and ability to chemisorb the CO(2) present at low concentrations in air. However, this chemisorption process is likely limited by internal diffusion of CO(2) into the bulk of K(2)CO(3). Therefore, the size of the K(2)CO(3) particles is expected to be an important factor in determining the kinetics of the sorption process during CO(2) capture. To date, the effects of particle size on supported K(2)CO(3) sorbents are unknown mainly because particle sizes cannot be unambiguously determined. Here, we show that by using a series of techniques, the size of supported K(2)CO(3) particles can be established. We prepared size-tuned carbon-supported K(2)CO(3) particles by tuning the K(2)CO(3) loading. We further used melting point depression of K(2)CO(3) particles to collectively estimate the average K(2)CO(3) particle sizes. Using these obtained average particle sizes, we show that the particle size critically affects the efficiency of the sorbent in CO(2) capture from air and directly affects the kinetics of CO(2) sorption as well as the energy input needed for the desorption step. By evaluating the mechanisms involved in the diffusion of CO(2) and H(2)O into K(2)CO(3) particles, we relate the microscopic characteristics of sorbents to their macroscopic performance, which is of interest for industrial-scale CO(2) capture from air.