Preparation and High-Temperature CO₂ Capture Properties of Nanocrystalline Na₂ZrO₃

A novel method for producing nanosized Na 2 ZrO 3 with well-controlled crystal phase has been developed, resulting in excellent kinetics for CO 2 capture at high temperatures. The novel preparation method involves a soft-chemical route starting with the generation of a complex from zirconoxy nitrate and sodium citrate, followed by a strong exothermic reaction between nitrate and citrate during calcination in a controlled atmosphere. The in situ produced carbon during the calcination serves as a dispersant of the oxide, and subsequent carbon burnoff promotes the formation of nanocrystalline Na 2 ZrO 3 with an open pore structure. The calcination temperature and atmosphere are very crucial for controlling the crystal phase of Na 2 ZrO 3 . The resulting sodium zirconate samples are characterized by XRD, N 2 adsorption, Hg porosimetry, and SEM. A two-step calcination at 1073 K results mainly in the monoclinic phase, whereas one-step calcination at 1073 K or higher enhances the formation of the thermodynamically stable phase, namely hexagonal Na 2 ZrO 3 . A kinetic study of CO 2 capture in a tapered element oscillating microbalance (TEOM) reactor has shown that the monoclinic Na 2 ZrO 3 is much more active than its hexagonal counterpart. The ability to work at CO 2 partial pressures as low as 0.025 bar, together with the excellent stability in multicycle capture/regeneration makes nanocrystalline Na 2 ZrO 3 a very promising CO 2 acceptor for different applications.