Encoding CO 2 Adsorption in Sodium Zirconate by Neutron Diffraction.

Recent research into sodium zirconate as a high-temperature CO 2 sorbent has been extensive, but detailed knowledge of the material's crystal structure during synthesis and carbon dioxide uptake remains limited. This study employs neutron diffraction (ND), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) to explore these aspects. An improved synthesis method, involving the pre-drying and ball milling of raw materials, produced pure samples with average crystal sizes of 37-48 nm in the monoclinic phase. However, using a slower heating rate (1 °C/min) decreased the purity. Despite this, the 1 °C/min rate resulted in the highest CO 2 uptake capacity (4.32 mmol CO 2 /g Na 2 ZrO 3 ) and CO 2 sorption rate (0.0017 mmol CO 2 /g) after 5 min at 700 °C. This was attributed to a larger presence of microstructure defects that facilitate Na diffusion from the core to the shell of the particles. An ND analysis showed that the conversion of Na 2 ZrO 3 was complete under the studied conditions and that CO 2 concentration significantly impacts the rate of CO 2 absorption. The TGA results indicated that the reaction rate during CO 2 sorption remained steady until full conversion due to the absorptive nature of the chemisorption process. During the sorbent reforming step, ND revealed the disappearance of Na 2 O and ZrO 2 as the zirconate phase reformed. However, trace amounts of Na 2 CO 3 and ZrO 2 remained after the cycles.