New approach to consecutive CO oxidation and CO2 chemisorption using Li2CuO2 ceramics modified with Na- and K-molten salts

Abstract

To analyze for the first time the effect of alkali carbonate addition to lithium cuprate during the consecutive process of carbon monoxide (CO) oxidation and subsequent carbon dioxide (CO₂) capture, a series of X-containing Li₂CuO₂ (X = Na and/or K) materials were prepared by mechanically adding different mixtures of sodium and potassium carbonates to lithium cuprate. According to results, the presence of carbonate allowed the improvement of both the CO conversion and the CO₂ chemisorption in a moderate temperature range, between 400 and 650 °C. According to the reaction mechanism proposed in this work, this enhancement was produced due to the formation of a new phase between the mechanically added Na and K carbonates and the Li carbonate produced during the CO₂ capture on the ceramic surface. The composition of this phase changes depending on the temperature used and the amount of lithium carbonate formed on the surface. Once the newly formed carbonate phase melts, the diffusion of both reactants (CO and O₂) is enhanced towards the bulk material, promoting the oxidation of CO and later CO₂ capture. Another benefit was detected on the ratio between CO₂ captured and released. According to this parameter, the samples modified with a single carbonate, Na- or K–Li₂CuO₂ samples, showed a high tendency to capture the CO₂ formed during the CO oxidation, allowing the simultaneous elimination of two toxic and harmful gases, CO and CO₂. The results are promising, considering that at an industrial level, two different materials are required for this process: a heterogeneous catalyst followed by a chemical adsorbent, which can be replaced with a single modified-Li₂CuO₂ material studied in this work.