Real time ICCU-RWGS performance using Ni-CaO based DFMs

During ICCU-RWGS, two key steps are involved, including the capture of CO2, and the regeneration of sorbent (simultaneous CO2 utilisation). The following work (https://doi.org/10.1016/j.seppur.2022.121604) reported ICCU-RWGS using Ni-based catalysts with different supports, focusing on the gas concentration at different reaction time.

“It is necessary to monitor the real-time ICCU-RWGS process to evaluate the CO₂ adsorption performance and catalytic activity. The promotion effect of support of Ni could be clearly demonstrated in the CO₂ adsorption stage, presenting as the enhanced CO₂ capture rate compared to the benchmark (SiO₂ line in Fig. 8a). Specifically, Ni/CeO₂-CaO and Ni/Al₂O₃-CaO exhibited superior CO₂ capture rate and capacity (∼9.58 and 9.31 mmol g-1 at 650 °C for ∼28 min), which was attributed to the abundant basicity of Ni/CeO₂ and Ni/Al₂O₃, as indicated in Fig. 5b.”

“Fig. 8. Real-time performance of various Ni/support-CaO BCMs over ICCU-RWGS at 650 °C: (a) CO₂ capture performance collected on TGA; (b) CO₂ conversion and CO selectivity; (c) CO generation rate and CO₂ conversion (d) under various temperature over Ni/CeO₂-CaO.” https://doi.org/10.1016/j.seppur.2022.121604

“The various Ni/support-CaO BCMs also exhibited distinct CO generation rates and real-time CO₂ conversion during the hydrogenation step. As shown in Fig. 8b and 8c, the Ni/CeO₂-CaO BCM could achieve an optimal real-time CO₂ conversion (∼60%) and CO generation rate (∼1.7 μmol s^-1g⁻¹) at 650 °C. The excellent Ni dispersion and stronger basicity of Ni/CeO₂ might contribute to the superior ICCU-RWGS performance. It is worth noting that Ni/TiO₂-CaO also exhibited outstanding real-time CO₂ conversion (∼57%), which might be attributed to the slowly released Ni from easily reducible NiTiO₃ spinel species (Fig. 3, Fig. 4) [50]. As a comparison, Ni/Al₂O₃ showed poorer catalytic activities, indicating that the nonreducible spinel (Fig. 3, Fig. 4a) played poor catalytic performance in ICCU.

In this work, we focused on the initial 1500 s of CO₂ conversion to evaluate the real-time gas production in ICCU-RWGS. The CO₂ desorption is relatively fast in the initial stage of the hydrogenation step (0–500 s), especially under higher temperature (e.g. 700 °C), which directly limits the CO₂ conversion rate at this stage (as shown in Fig. 8e and 8f). Since only 5% H₂/N₂ was used in this work, excessive CO₂ release would decrease the ratio of H₂:CO₂ and affect the equilibrium of RWGS reaction. After the rapid decomposition of the surface layer of CaCO₃, the release of CO₂ and the performance of RWGS is gradually stabilised until the carbonates are thoroughly consumed.”