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

Abstract

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 PCO2. Results indicated that all the samples were able to chemisorb CO2 (if PCO2 ≥ 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.