For ICCU research, most of the catalysts are not noble metal-based. However, Ru- and Rh- based catalysts are considered for the development of dual functional materials for ICCU-methanation. These catalysts still have much higher costs than Ni- or Fe-based DFMs. However, the noble-based DFMs have much higher efficiency than Ni- and Co-based DFMs, as indicated in the following figure (https://doi.org/10.1016/j.jcou.2016.05.003). In addition, Ru- and Rh- based catalysts might be promising for low-temperature and medium-temperature applications.
Fig. 2. Concentration of CH4 in the product stream (dry basis) for various supported metal catalysts. Feed: 4% CO2/16% H2/He, P = 1 atm. (https://doi.org/10.1016/j.jcou.2016.05.003)
The following sentences are copied from this reference (https://doi.org/10.1016/j.ccst.2022.100052) regarding the use of Ru- and Rh-based DFMs for ICCU-methanation.
“The feasibility study of the Ru-based DFMs was first conducted and pioneered by Farrauto and co-workers (Duyar et al., 2015). Ru supported on γ-Al2O3 has been widely reported to be effective for CO2 methanation. After the addition of CaO, the sorbent/catalyst composites produced much more CH4 than the Ru/γ-Al2O3. A similar result was also reported by Bermejo-López et al. (Bermejo-López et al., 2019a), which showed the dual functionality of the material. Yet CO2 methanation on CaO/γ-Al2O3 was not observed, indicating the synergistic effect of the sorbent and catalyst in DFMs. With an increase in the CaO:Ru in the DFMs, a greater extent of CO2 spillover and methanation was observed. The optimum performance was reached for 5%Ru-10%CaO/γ-Al2O3 in terms of the CH4 yield per kg of DFM. By changing the active metals as well as the sorbent materials, the performances of DFMs were further investigated by Farrauto et al. (Duyar et al., 2016). The CH4 capacity of the 0.1%Rh-10%CaO/γ-Al2O3 was found to be similar to that of 5%Ru-10%CaO/γ-Al2O3 (0.4 vs. 0.5 g-mol/kg), possibly due to the higher methanation activity of Rh at lower temperatures. Nonetheless, the Ru-based DFMs showed a faster reaction rate of methanation than Rh-based DFMs, as the methane generation peak was sharp and completed within 25 min on 5%Ru-6.1%Na2O/γ-Al2O3 compared to ∼ 35 min for 0.5%Ru-6.1%Na2O/γ-Al2O3 (Arellano-Treviño et al., 2019a). Considering the lower price ($19.9 USD/g for Ru vs. $498.3 USD/g for Rh) (Daily Metal Prices, 2022) and higher stability of Ru, Ru-based DFMs are still promising compared to the Rh-based DFMs (Arellano-Treviño et al., 2019a; Duyar et al., 2016).”