Reaction mechanisms of Ru-based DFMs for ICCU-methanation

The following sentences are copied from this reference ( regarding the reaction mechanism of Ru-based DFMs.

“For the mechanism of the CO2 capture and methanation on Ru-based DFMs, Farrauto et al. (Duyar et al., 2015Zheng et al., 2016) proposed that CO2 is mainly chemisorbed on CaO sites and spillover to the Ru sites upon H2 introduction. Due to the methanation activity of Ru, CO2 can then be reduced by H2 for the generation of CH4 on the Ru surface as shown in Fig. 15. An in-situ DRIFTS study was conducted to elucidate the possible mechanism of 5%Ru-6.1%Na2O/Al2O3 DFM (Proaño et al., 2019). During the capture stage on the 5%Ru/Al2O3 surface, CO2 was absorbed on the Al2O3 OH groups and the Ru sites. After the addition of Na2O, the CO2 was mainly absorbed on Al-O-Na+ sites with the formation of bidentate carbonates. The adsorbed bicarbonates and bidentate carbonates spillover to the Ru-support interface for methanation with the formate species as intermediates, as shown in Fig. 16. Nonetheless, it was assumed that the carbonyl was the intermediate on 1%Ru/Al2O3, while on the 5%NaNO3/1%Ru/Al2O3, both carbonyl, formate, carbonate, and biocarbonate species were likely to be the reaction intermediates for methanation (Park et al., 2021). On Li-Ru/Al2O3 DFM, in-situ DRIFTS and TG-MS indicated that the formed Li-Al phases could facilitate the prompt sorption of CO2 in the form of bidentate carbonates, with further adsorbed CO2 being absorbed as weakly bonded bicarbonates at a slower rate (Cimino et al., 2022). The spillover mechanism of CO2 from Li-Al oxide to Ru sites for methanation was also confirmed by in-situ DRIFTS in this study.”


Fig. 15. Schematic mechanism of the CO2 capture and methanation on Ru-CaO/Al2O3 DFM (Zheng et al., 2016).


Fig. 16. The proposed CO2 methanation mechanism on 5%Ru/Al2O3 (right side) and 5%Ru-6.1%Na2O/Al2O3 (left and right side) (Proaño et al., 2019).

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