CaO-Based CO2 Sorbents with a Hierarchical Porous Structure Made via Microfluidic Droplet Templating

Calcium looping, a CO2 capture technique based on the cyclic carbonation and calcination of CaO, is a promising short- to midterm solution to reduce CO2 emissions. However, CaO suffers from sintering under industrially relevant operating conditions, which reduces rapidly its cyclic CO2 uptake capacity. Here, we report the design and manufacture of a hierarchical, porous (HP) CaO-based CO2 sorbent. The hierarchically porous sorbent is created through the assembly of calcium carbonate nanoparticles and monodisperse oil droplets generated via microfluidic emulsification. The structure of the sorbent is stabilized by an Al2O3 coating via atomic layer deposition (ALD). The sorbent outperformed the CO2 uptake of the reference limestone by ca. 140%. The improved CO2 uptake capacity is attributed to (i) the stabilization of the micro- and mesoporous structure of the material by the formation of Ca-Al mixed oxides, that is, Ca12Al14O33 and Ca3Al2O6, and (ii) an improved mass transport within the sorbent particles owing to the HP structure of the material.