Ru-Ba synergistic effect in dual functioning materials for cyclic CO2 capture and methanation

Abstract

Mechanistic aspects involved in cyclic CO2 capture and methanation were analyzed by comparing the catalytic behavior of a Ru-BaO/Al2O3 (intimate mixture) with that of a mechanical mixture of BaO/Al2O3 + Ru/Al2O3. Both combinations showed similar performance in the storage of CO2 and in the thermal stability of adsorbed species: CO2 is strongly adsorbed over the BaO component, and cannot be completely released even at high temperatures. The H2 reactivity of the stored species is strongly enhanced for the intimate mixture, showing increased CH4 formation at lower temperatures thus indicating the synergistic effect between the storage and hydrogenation functions. Dual Function Material (DFM) experiments performed in the presence of O2 and steam during the CO2 capture step showed a decrease in the amounts of adsorbed CO2 and a lower methanation rate. When NOx is also present during the capture step, the adsorption of CO2 is hindered by strongly adsorbed NOx. However, while Ru-BaO/Al2O3 can be fully regenerated by H2, BaO/Al2O3 + Ru/Al2O3 suffers from deactivation due to the buildup of adsorbed NOx. It should be understood that in power plant applications the DFM will be located downstream from SCR and therefore the level of NOx will be in the ppm level. Furthermore, it is completely desorbed as NH3 and N2 upon the addition of H2 and thus will not have a significant impact of overall performance for CO2 capture and conversion.