Elucidating the structural evolution of highly efficient Co–Fe bimetallic catalysts for the hydrogenation of CO₂ into olefins

Constructing Co-Fe bimetallic catalyst is of high research value for CO₂ conversion based on its outstanding traits, however, its activity-structure relationship is still confusing. Herein, a series of Na-promoted Co-Fe bimetallic catalysts differing in composition or proximity were prepared and their structural evolution during reduction and reaction was elucidated. It was found that the Co1Fe2 catalyst with Co/Fe molar ratio of 1/2 and close proximity was conducive to rapid reduction of CoFe₂O₄ to Co_xFe_y alloy, and further carbonization to stable χ-(Co_xFe_1−x)₅C₂ alloy carbide as the active phase for olefin formation, thus exhibiting superior performance without evident deactivation for over 500 h on-stream. Especially at high space velocity, it achieved an unprecedented olefin space-time yield up to 1810.8 mg·g_cat⁻¹·h⁻¹, showing a potential application in micro-channel reactor. Moreover, the alloy carbide plays a unique role in facilitating CO₂ adsorption, and inhibiting the hydrogenation of surface intermediates as well as suppressing carbon deposition.