Thermokinetic and microstructural analyses of the CO₂ chemisorption on K₂CO₃-Na₂ZrO₃

Sodium zirconate (Na₂ZrO₃) was synthesized via a solid-state reaction. Subsequently, a portion of the prepared Na ₂ZrO₃ was mechanically mixed with 5 wt.% potassium carbonate (K₂CO₃). The Na₂ZrO₃ and K-Na₂ZrO₃ samples were characterized, and the CO ₂ capture processes were evaluated. The potassium addition did not modify the structural or microstructural characteristics of the Na ₂ZrO₃. However, during CO₂ chemisorption, the material presented some important variations that depended on the potassium addition. The maximum CO₂ capture of the Na₂ZrO ₃ sample was observed at T ≥ 550 C, while the CO₂ capture of the K-Na₂ZrO₃ sample was significantly favored at 400 C. According to DSC analysis, the CO₂ capture increase observed at lower temperatures was due to the formation of a K-Na carbonate eutectic phase. Additionally, for the samples demonstrating effective CO ₂ capture at relatively low temperatures, SEM microstructural analysis demonstrated the formation of a Na₂CO₃-ZrO ₂ mesoporous external shell. Moreover, some kinetic parameters were determined. The isothermal data were fitted to a double exponential model related to the direct CO₂ chemisorption (k₁) and diffusion processes (k₂). The K-Na₂ZrO₃ sample presented higher k₁ and k₂ values than Na₂ZrO ₃ at all temperatures investigated, confirming that the potassium addition improved the CO₂ capture process. Further, the potassium in Na₂ZrO₃ significantly enhanced the CO₂ capture at approximately 400 C, in comparison to the Na₂ZrO₃ sample. Finally, it was observed that potassium negatively compromised the chemisorption of CO₂ after several cycles, due to potassium segregation and sublimation.