Unlocking the role of Ni-Fe species in CO2 methanation

The conversion of CO2 to methane has garnered immense interest, owing to its pivotal roles in reducing carbon emissions and producing environmentally friendly natural gas. This study explores the application of 13X zeolite-supported Ni-Fe catalysts with varying Ni/Fe ratios in CO2 methanation. Structural analyses reveal the formation of Ni-Fe alloy species. Specifically, the Ni-Fe species induce a high binding energy shift for Fe and a low energy shift for Ni species. Additionally, the presence of Ni-Fe species results in a slight increase in the reduction temperature for Ni species, while significantly lowering the reduction temperature of Fe species. Comparative assessments demonstrate that Ni-Fe species exhibit diminished hydrogenation activity in comparison to monometallic Ni species, resulting in reduced CO2 conversion and CH4 selectivity with increased Fe/Ni ratios. Notably, 5Ni-5Fe-13X and 2Ni-8Fe-13X catalysts display heightened activity in the conversion of CO2 to CO and ethane. Furthermore, this study finds that the blockage of micropores does not significantly affect the catalyst's methanation activity, suggesting the small metal species in the micropores did not promote the CO2 methanation activity. In situ DRIFTS reveals that the formate intermediate is promoted by the presence of Ni species, whereas the formation of CO intermediate is facilitated by Ni-Fe species. These insights deepen our grasp of the structural and catalytic attributes inherent to Ni-Fe species in the context of CO2 conversion, fostering a more comprehensive understanding of their functionality in this critical process.