Tuning Na2ZrO3 for fast and stable CO2 adsorption by solid state synthesis

This work assessed the possibility to tune the CO2 capture performance of Na2ZrO3 with respect to CO2 uptake and CO2 sorption rate by varying the conditions used in the solid-state synthesis. The resulting Na2ZrO3 were characterized by XRD, SEM-EDS, XPS and TGA. A structural, chemical, microstructural and kinetic analysis of the Na2ZrO3–CO2 system over one cycle was performed to identify the correlation with the sorbent performance. The heating rate, the molar ratio of the Na2CO3 and ZrO2 used in the synthesis of Na2ZrO3, as well as additional powder processing steps of the reactants, all had a major impact on the sorbent's CO2 capture performance. The best performing sorbent with the highest CO2 uptake capacity (4.83 mmol CO2/g) and absorption rate (30. 5 nmmol/s) at 700 °C was obtained when the Na2CO3 and ZrO2 reactants were processed by ball milling varying the molar ratio of 1:1 and a synthesis heating rate of 1 °C/min. Under these conditions, the optimised Na2ZrO3 exhibited 86.5% conversion in 10 min with respect to the theoretical value. Na2ZrO3 synthesised using the optimised conditions as listed above were constructed with nanocrystals of ~ 20 nm in average diameter as observed using XRD (Sherrer's formula). The Na2ZrO3 synthesised in this study favoured the ionic solid-state diffusion of Na and O from the core to the surface of the material to readily react with CO2. Moreover, an excellent cyclic stability of the sorbent over 70 sorption/desorption cycles was noted after an initial decay when the CO2 cycles were shortened to 5 min.