Dynamic structural evolution of iron catalysts involving competitive oxidation and carburization during CO2 hydrogenation

Abstract

Identifying the dynamic structure of heterogeneous catalysts is crucial for the rational design of new ones. In this contribution, the structural evolution of Fe(0) catalysts during CO 2 hydrogenation to hydrocarbons has been investigated by using several (quasi) in situ techniques. Upon initial reduction, Fe species are carburized to Fe 3 C and then to Fe 5 C 2 . The by-product of CO 2 hydrogenation, H 2 O, oxidizes the iron carbide to Fe 3 O 4 . The formation of Fe 3 O 4 @(Fe 5 C 2 +Fe 3 O 4 ) core-shell structure was observed at steady state, and the surface composition depends on the balance of oxidation and carburization, where water plays a key role in the oxidation. The performance of CO 2 hydrogenation was also correlated with the dynamic surface structure. Theoretical calculations and controll experiments reveal the interdependence between the phase transition and reactive environment. We also suggest a practical way to tune the competitive reactions to maintain an Fe 5 C 2 -rich surface for a desired C 2+ productivity.