Relationship between structural properties and CO₂ capture performance of CaO-based sorbents obtained from different organometallic precursors

A series of CaO-based sorbents were synthesized from various organometallic precursors, namely, calcium propionate, calcium acetate, calcium acetylacetonate, calcium oxalate, and calcium 2-ethylhexanoate, by a simple calcination technique. In general, the five organometallic precursors (OMPs) exhibit a three-step weight loss regime in their respective thermogravimetic (TG) profiles. The first weight loss occurs because of dehydration in the temperature range of 50-200 °C. The second one results from decomposition leading to the formation of calcium carbonate in the temperature range of 450-550 °C. The calcium carbonate so formed then undergoes decarboxylation at higher temperatures of 710-750 °C and results in the formation of calcium oxide. Among the various precursors evaluated, CaO-sorbents obtained from calcium propionate and calcium acetate precursors were found to exhibit the highest CO₂ capture capacity. The observed results were correlated with the intrinsic properties of the precursors by means of various techniques like thermogravimetric analysis (TGA), pore-size distribution (PSD), and differential scanning calorimetry (DSC). It was found that these two sorbents possessed higher surface area and larger pore volume compared to other sorbents prepared in this work. Thermal decomposition of these two OMPs resulted in the maximum evolution of heat, which could eventually lead to the generation of larger macropores, thus explaining the resultant CO₂-uptake capacity we observed. Interestingly, the CO₂ capture capacity of the sorbents was found to be directly proportional to the porosity per unit surface area. In summary, we were successful in correlating the intrinsic properties of an OMP to the eventual CO₂ capture capacity of the sorbent. From the present investigation, it seems that the amount of heat evolved during the course of decomposition plays a direct role in the resultant porosity and thereby regulates the eventual CO₂ capture capacity.