Elemental Fe conditioning for the synthesis of highly selective and stable high entropy catalysts for CO2 methanation

High entropy oxides (HEOs) with high stability and designability have demonstrated excellent catalytic performance in CO2 hydrogenation. However, it is challenging to combine high methane selectivity and high stability of HEOs using an equimolar design strategy. In this study, a non-equimolar design strategy was used to fix the Cr, Co, Mn and Ni elements and adjust different Fe molar amounts to prepare a highly crystalline HEO at 900 °C. After H2 reduction, the catalyst (HEO-4-900/H2) achieved 72.9% CO2 conversion and 98.8% methane selectivity at atmospheric pressure and 400 °C, and maintained a high methane selectivity of over 97% after 100 h stability test. The catalytic activity was influenced by the amount of Fe. Increasing the amount of Fe could precisely regulate the crystallinity and oxygen defects of the crystal, improve the catalyst stability, reduce the interaction between the Co-Ni alloys and HEOs, and allow the catalyst to contain more Co-Ni active sites and more abundant oxygen vacancies. This study demonstrates the considerable potential of HEOs for CO2 methanation, and provides a new design idea for further stimulating highly active CO2 methanation HEOs catalysts.