Tuning the Electronic Structure of FeCoNiCuMn High-Entropy Alloys by Ni Content for CO2 Methanation

High-entropy alloys (HEAs), as a novel type of catalytic material, have shown broad application prospects in the field of thermal catalytic CO2 hydrogenation due to their excellent thermal stability and tunable electronic structure. However, the current research on their application in the CO2 methanation reaction remains quite limited. In this paper, a series of FeCoNixCuMn (x = 15, 20, 25, 30, 35 at. %) HEA catalysts were successfully synthesized by a solvothermal method combined with thermal reduction. A systematic evaluation of their activity in CO2 methanation was subsequently conducted. The prepared HEAs presented a predominantly FCC solid-solution structure and coral-like porous morphology, with a uniform distribution of each metal element. By adjusting the Ni content, the electronic structure, the concentration of unpaired electrons, and the adsorption behavior of H2 and CO2 of the HEAs can be effectively regulated. Among them, the FeCoNi25CuMn HEAs exhibited the best catalytic performance and maintained good stability during a 120 h stability test. In situ diffuse reflectance infrared Fourier transform spectroscopy combined with density functional theory calculations reveals that the CO2 methanation reaction over FeCoNi25CuMn follows the pathway of CO2 → COOH* → CO* → CHO* → CH3* → CH4. An appropriate Ni content adjusted the d-band center of the HEAs to –1.18 eV, which ensured the activation of CO2 and simultaneously promoted the desorption of products. This work has verified the feasibility of HEAs as CO2 methanation catalysts and provided an experimental and theoretical basis for the rational design of multicomponent catalysts for carbon resource utilization.