Encoding CO Adsorption in Sodium Zirconate by Neutron Diffraction.

Recent research into sodium zirconate as a high-temperature CO 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 uptake capacity (4.32 mmol CO/g NaZrO) and CO sorption rate (0.0017 mmol CO/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 NaZrO was complete under the studied conditions and that CO concentration significantly impacts the rate of CO absorption. The TGA results indicated that the reaction rate during CO 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 NaO and ZrO as the zirconate phase reformed. However, trace amounts of NaCO and ZrO remained after the cycles.