Proposed mechanism of Ni/CeO2-CaO based ICCU-methanation

https://doi.org/10.1016/j.cej.2022.135394

“From our experimental results and DFT calculation, the mechanism of CO₂ methanation over Ni/CeO₂ catalysts can be summarized as follow (Fig. 7): Firstly, CO₂ molecules are chemisorbed on the partially reduced NiO-CeO₂ interface, where most of the C = O bonds are broken together with the oxygen transferring to the ceria support to restore the oxygen balance. These oxygens move around in the ceria lattice through the abundant vacancies and provide available sites for further CO₂ chemisorption. Afterwards, different reaction pathways will be created. A fraction of carbon species are converted to CO through the reverse water gas shift reaction and then hydrogenated to CH₄; simultaneously, part of the oxygens removed upon the double bonds breaking are replaced by catalyst oxygen and released as CO or CO₂, leaving reduced sites on the catalyst again. Therefore, the main products of Ni/CeO₂ sub-nanometer catalysts are CO and CH₄.”

“Fig. 7. Reaction mechanism during the ICCU process: (a) CeO₂-CaO, (b) Ni/CeO₂-CaO.”