Encoding CO₂ Adsorption in Sodium Zirconate by Neutron Diffraction

Recent research into sodium zirconate as a high-temperatureCO₂ sorbent has been extensive, but detailed knowledge of thematerial’s crystal structure during synthesis and carbon dioxide uptake remainslimited. This study employs neutron diffraction (ND), thermogravimetricanalysis (TGA), and X-ray diffraction (XRD) to explore these aspects. Animproved synthesis method, involving the pre-drying and ball milling of rawmaterials, produced pure samples with average crystal sizes of 37–48 nm in themonoclinic phase. However, using a slower heating rate (1 °C/min) decreased thepurity. Despite this, the 1 °C/min rate resulted in the highest CO₂ uptakecapacity (4.32 mmol CO₂/g Na₂ZrO₃) and CO₂ sorptionrate (0.0017 mmol CO₂/g) after 5 min at 700 °C. This was attributedto a larger presence of microstructure defects that facilitate Na diffusionfrom the core to the shell of the particles. An ND analysis showed that theconversion of Na₂ZrO₃ was complete under the studiedconditions and that CO₂ concentration significantly impacts therate of CO₂ absorption. The TGA results indicated that thereaction rate during CO₂ sorption remained steady until fullconversion due to the absorptive nature of the chemisorption process. Duringthe sorbent reforming step, ND revealed the disappearance of Na₂Oand ZrO₂ as the zirconate phase reformed. However, traceamounts of Na₂CO₃ and ZrO₂ remainedafter the cycles.