To alleviate the environmental concerns regarding the current CO₂ emissions into the atmosphere Carbon Capture & Storage (CCS) is investigated as one of the possible routes. Due to the acidic character of CO₂, basic oxides are expected to be suitable sorbents. We investigated the use of hydrotalcites (HT) as CO₂ sorbent. HT, e.g. Mg₄Al₂(OH)₁₂CO₃.4H₂O, has a structure similar to that of Mg(OH)₂. In the latter, Mg²⁺ is octahedrally coordinated by hydroxyl group, which are edge-shared to form a sheet-like structure. A net positive charge of the brucite-like layers originates from replacement of Mg²⁺ by Al³⁺. This charge is compensated for by anions, typically carbonate, situated together with water molecules in the interlayer. In the current contribution we will report on the relation between CO₂ capture properties and HT platelet size. Two different series samples were prepared i.e., unsupported HTs with lateral size range from 40 nm to 2 mm, very small (~20 nm) supported HTs were deposit on carbon nanofibers (CNF).

The CO₂ absorption characteristics of unsupported HTs at 250 °C showed a low and invariant absorption capacity (0.1 mmol•g^-1) for all samples regardless of the platelet size. However, small supported hydrotalcites showed a considerable higher uptake (1.3 mmol•g^-1) of CO₂. Currently we tentatively relate this higher uptake to a higher density of defects in the Mg(Al)O_x phase that binds CO₂. Moreover, supported hydrotalcites gave improved cycle stability. We speculate that by anchoring individual HT platelets on CNF their mobility is limited, resulting in less agglomeration and annealing of defects on the Mg(Al)O_x phase, thus less deactivation upon cycling. These results indicate the advantage of supported hydrotalcites for the uptake of CO₂ capture. We improved not only the specific capacity by a factor 10 for the CO₂ capture material hydrotalcite, we also improved mechanical strength and cycle stability for these CO₂ capture materials.

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