Elemental Fe Conditioning for the Synthesis of Highly Selective and Stable High Entropy Catalysts for CO2 Methanation

•HEOs were an effective catalyst for CO2 methanation.•The catalytic activity of non-equimolar HEOs was superior to that of equimolar HEO.•Appropriate increase of Fe molar amount could improve the crystallinity and oxygen defects of HEOs.•Appropriate increase of Fe molar amount could reduce the interaction of Co-Ni oxides with HEOs.