Influence of support for LaNiO3-based DFMs on ICCU-methantion

https://doi.org/10.1016/j.fuel.2022.123842

“Catalytic activities of LaNiO₃-derived DFMs are evaluated by analyzing the evolution of CH₄ and CO production per cycle with reaction temperature (Fig. 7). These parameters were estimated applying Eqs. (2–3) for the data obtained from similar CO₂ adsorption and hydrogenation experiments to that reported in Fig. 6. Aiming to mimic an effluent gas from a combustion process, the CO₂ concentration during storage period was increased from 1.4 to 10% in these experiments, in which the carbon balance closed with an error below 5%.”

“Fig. 7. Evolution of: a) CH₄ and b) CO productions with temperature for DFMs obtained after the controlled reduction 30% LaNiO₃/CeO₂, 30% LaNiO₃/La-Al₂O₃, 30% LaNiO₃/Al₂O₃ and LaNiO₃ precursors.” https://doi.org/10.1016/j.fuel.2022.123842

“As can be observed in Fig. 7a, the evolution of CH₄ production with reaction temperature is influenced by the type of perovskite-based formulation used as precursor of the corresponding DFM in each experiment. As expected, methane production increases up to 440 °C for DMFs obtained after the reduction of bulk LaNiO₃ and 30% LaNiO₃/CeO₂ formulations. Above this temperature, CO₂ conversion slightly decreases due to a destabilization of adsorbed carbonates. In contrast, DFMs obtained from alumina-supported perovskites (30% LaNiO₃/Al₂O₃ and 30% LaNiO₃/La-Al₂O₃) achieve their maximum CH₄ production at 280 °C. Then, a progressive decrease in the amount of CH₄ produced is observed at increasing temperatures. As previously observed, weak strength basic sites are predominant for alumina-supported DFMs (Table 3). Thus, the maximum CH₄ production observed at 280 °C is related to a more efficient CO₂ adsorption on weak strength basic sites, main adsorption sites at this temperature range. On the contrary, as the reaction temperature increases, the adsorbed CO₂ on weak basic sites become less stable, limiting their hydrogenation for alumina-supported samples. Meanwhile, the presence of higher strength basic sites for non– and ceria-supported samples favours decomposition of a major quantity of the adsorbed CO₂ species to be hydrogenated to CH₄ at higher temperatures. Thus, Ni-La₂O₃ interface higher accessibility can be considered as a key parameter to maximize CO₂ adsorption and in-situ hydrogenation at this temperature range.

Regarding to CO formation (Fig. 7b), all samples show an increasing CO production with reaction temperature. This trend is ascribed to the promotion of the RWGS reaction (Eq. (17)) during the CO₂ hydrogenation step. In any case, the CO production is below 31 µmol g⁻¹ for all samples, which remarks the high selectivity towards methane of here developed materials.

Among different samples, the DFM obtained after the reduction of the LaNiO₃ formulation exhibits the highest CH₄ production (117 µmol g⁻¹), in line with the higher density of medium basic sites identified in Table 3. However, the DFM derived from 30% LaNiO₃/CeO₂ precursor maintains the highest CH₄ production, if the whole temperature range is considered. Furthermore, this sample shows a CO production 3 times lower (8 vs. 31 µmol g⁻¹) than the DFM obtained from bulk perovskite, which is ascribed to the higher strength of CO₂ adsorbed species [50], [51].”

“Table 3. Deconvoluted CO₂ desorption related to different basic sites, medium basic sites density and adsorbent utilization factor for bulk LaNiO₃ perovskite (LNO) and, 30% LaNiO₃/CeO₂, 30% LaNiO₃/Al₂O₃ and 30% LaNiO₃/La-Al₂O₃ samples after reduction in 5% H₂/Ar.”