Support and Size Effects of Activated Hydrotalcites for Precombustion CO₂Capture

A series of Mg−Al hydrotalcites (HTs) with lateral platelet sizes ranging from 40 nm to 2 μm were prepared hydrothermally. Small HT platelets (∼20 nm) were obtained by deposition onto a carbon nanofiber (CNF) support. The CO 2 sorption capacity at 523 K for the activated unsupported HT was low (∼0.1 mmol·g −1 ), regardless of the platelet size of the HT precursor. In addition, no relation was found between the CO 2 sorption properties of activated HTs and their specific surface area. The sorption capacity of the activated CNF-supported HTs was increased, depending on the HT loading, by an order of magnitude (1.3−2.5 mmol·g HT −1 ) compared to that of the activated unsupported HT. We propose that the CO 2 sorption capacities of HTs are determined by the amounts of low-coordination oxygen sites in the Mg(Al)O x nanoparticles, which is highest on supported HTs.