CO₂–CO capture and kinetic analyses of sodium cobaltate under various partial pressures

Sodium cobaltate and some Fe-containing samples were evaluated on the CO, CO₂ and CO–CO₂ sorption at high temperatures and low CO₂ partial pressures, in the presence and absence of oxygen. Initially, CO₂ chemisorption on these samples was analyzed using different P_CO2. Results indicated that all the samples were able to chemisorb CO₂ (if P_CO2 ≥ 0.2), where Fe-containing NaCoO₂ samples clearly showed higher CO₂ chemisorption efficiencies than pristine NaCoO₂. These results were explained by the partial iron reduction and the consequent oxygen release. When oxygen was added the chemisorption process was improved as a result of an iron reduction–oxidation mechanism. These results were confirmed kinetically by the Jander-Zhang and Eyring models. The temperature for complete CO catalytic conversion was shifted to lower temperatures as a function of iron content. Finally, simultaneous CO₂ and CO sorption as well as catalytic experiments were tested (in absence or presence of O₂). These results showed that CO was mainly oxidized and chemically captured, over the CO₂ direct capture, in oxygen absence and presence. Iron is able to release and capture oxygen by reduction–oxidation effect and facilitates oxygen dissociation for the carbonation process, through the Mars van Krevelen reaction mechanism.