Iron is known to produce hydrocarbons from CO2hydrogenation. One such popular approach utilizes the reverse water-gas shift (RWGS) reaction, followed by Fischer-Tropsch (FT) synthesis. Many attempts have been made to modify and improve its reactivity by addition of a second metal acting as a promoter. Understanding the effects of a promoting second metal via traditional impregnation or co-precipitation techniques is often challenging due to potential to form multiple coexisting phases and structures. In this work we studied the effect of adding ruthenium to iron by synthesizing ruthenium-iron oxide colloidal heterodimers, where the two elements are present in the form of nanoparticles, and in intimate contact with each other. Catalytic measurements coupled with in-situand ex-situcharacterization demonstrated that the addition of an intimate ruthenium phase in close proximity to iron leads to the reduction of iron oxide via a proximal hydrogen spillover effect, providing the active iron/iron carbide phase for the reaction at much lower temperatures than in iron oxide catalysts. Such an effect is not achievable in materials where Ru and Fe phases are separated at longer length scales. We also observed the transformation of the heterodimers into core-shell structures upon reduction due to the encapsulation of ruthenium by iron carbide. More generally, we demonstrated that other intimately contacted noble metals can activate FeOxin a similar way. The well-defined structure of our starting materials enabled us to study the cooperative mechanism of ruthenium promotion in iron-based catalysts and its implications for the catalytic performance in CO2hydrogenation processes.

Ruthenium-iron oxide colloidal heterodimers unravel promotion mechanism in iron-catalyzed CO2 hydrogenation to hydrocarbons

2019 Fall National Meeting

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