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

Abstract

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 CoxFey alloy, and further carbonization to stable χ-(CoxFe1−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·gcat−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.