Hydrotalcite based Ni–Fe/(Mg, Al)Ox catalysts for CO2 methanation – tailoring Fe content for improved CO dissociation, basicity, and particle size

Abstract

It is essential for mankind to address greenhouse gas emission, depletion of fossil resources and development of efficient storage and transportation of renewable energy. By using the atmospheric gas CO₂ as raw material for the value-added chain, an overall CO₂ neutral circular economy is imaginable. The power to gas (PtG) concept tackles all three topics by producing methane as energy carrier using renewable hydrogen and capture of CO₂. Methanation has been known for decades; however, the preparation of noble metal free catalysts possessing high activity, selectivity and stability remains challenging. Bimetallic Fe_xNi_x−1 alloy catalysts have shown synergistic effects for methanation as they can be tailored to the CO dissociation energy. Multicomponent hydrotalcite precursors allow close proximity of the individual metals enabling high dispersion and continuous variation of the composition. Herein, we studied Ni–Fe/(Mg, Al)O_x bimetallic catalysts derived via mixed hydrotalcite precursors. Iron has a significant influence on both activity and selectivity due to small particle sizes, facilitated CO dissociation, and tailored surface basicity. For the best catalyst (Fe/Ni = 0.1), the CO₂ conversion rate reaches about 6.96 mmol CO₂ mol_Fe+Ni⁻¹ s⁻¹ at 335 °C with a selectivity of 99.3% to CH₄, remaining constant for at least 24 h time on stream.