Showing papers by "Luca Lietti published in 2021"

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.

Storage Material Effects on the Performance of Ru-Based CO2 Capture and Methanation Dual Functioning Materials

Abstract: In this study, a systematic investigation on Dual Functioning Materials (DFMs) for the capture and methanation of CO₂ is carried out The attention is focused on the nature of the CO₂ adsorbent component (storage material, SM) varying between alkaline (Li, Na, K) and alkaline-earth (Mg, Ca, Ba) metal oxides in combination with Ru, both supported on an Al₂O₃ support Combining gas phase reactivity analysis and FT-IR characterization, the samples are characterized in terms of CO₂ storage capacity It is found that all the SM-containing samples adsorb significant amounts of CO₂ as carbonate species, with the higher amounts being adsorbed when the more thermally stable species are formed, ie, when Ca, Ba, or K are employed as SMs In all cases, the hydrogenation of the adsorbed carbonates to CH₄ occurs at lower temperature, if compared to their thermal desorption However, in the case of Ca- and Ba-based DFMs, resilient carbonates are present on the material surface It was found that the SMs able to form the more thermally stable carbonates upon CO₂ adsorption also showed the best performances in capture/methanation cycles at 350 °C, even if some residual carbonates were left on the DFM after the hydrogenation step In particular, the following order of reactivity has in fact been observed in terms of CH₄ production: Ru–K ≥ Ru–Ba > Ru–Ca > Ru–Na ≫ Ru–Mg ≅ Ru–Li ≅ Ru The presence of steam and O₂ during the capture step has a detrimental effect on the CO₂ adsorption for all samples and, as a result, on CH₄ production due to the competition of CO₂ and water for the same adsorption sites Thus, only SMs able to form strongly bound carbonates species upon CO₂ exposure can retain significant CO₂ storage capacity also in the presence of water in the adsorption feed