Different alkali-promoted 1%Ru/Al2O3 dual functional materials were studied for integrated CO2 capture and methanation. Li was found to show the best performance (https://doi.org/10.1016/j.jcou.2019.12.010). The ICCU tests were carried out at 230 °C and the gas feeding was switched between 15% CO2 and 12% H2 balanced with Ar. In addition, gas analysis was done by the mass spectrometer. The ICCU results are shown in the following figure:
TG-MS results of ICCU-methanation over Li-Ru/Al and Na(N)-Ru/Al catalysts (https://doi.org/10.1016/j.jcou.2019.12.010)
The following sentences are copied from this reference (https://doi.org/10.1016/j.ccst.2022.100052) regarding the influence of Li, Na and K addition for ICCU-RWGS.
“The effects of Li (1.73%), Na (4.34%), and K (5.66%) addition in the 1%Ru/Al2O3 were investigated on its capture/methanation performance (Cimino et al., 2020). It appeared that the Li-modified sample showed higher methanation activity (H2 and CO2 co-feeding test) compared to its Na and K doped counterparts. The CO2 uptake capacity was found to be increased in the order of Na ≤ K < Li. The integrated capture/methanation experiments showed a much higher CH4 generation rate for Li-Ru/Al than that for Na-Ru/Al, indicating the effectiveness of the developed Li-Ru/Al in the ICCC-Met process. The stable cyclic operation with the generation of pure CH4 could be achieved at the temperature as low as 230°C. With the addition of Li to the Ru/Al2O3, mixed Li-Al phases (LiAl5O8, LiAlO2, and Li2Al4(CO)3(OH)12-3H2O) were formed. These phases have been reported to suppress the formation of highly stable carbonate species that were difficult to hydrogenate, and the synergism was found between the Li-Al phases and the Ru size, which enhanced the methanation activity of the DFM (Cimino et al., 2022). In another study, different alkali (Li, Na, K) and alkaline earth metals (Mg, Ca, Ba) were investigated for their effects on the capture and methanation performance of 1%Ru/γ-Al2O3 at the operation temperature of 350°C (Porta et al., 2021a). The molar ratio of different sorbent metals was constant compared to Ru (∼ 14). However, different results were reported from the previous study (Cimino et al., 2020). It was found that the Li-modified DFM showed similar performance to Ru/γ-Al2O3, being worse than other metals modification. The Ru and Ru-Li samples were reported to lack sorption sites for CO2 at 350°C based on CO2-TPD and H2-TPSR tests. In terms of the CH4 yield, the modification promotion was in the order of Ru-K > Ru-Ba > Ru-Ca > Ru-Na >> Ru-Mg > Ru-Li ≈ Ru.”