Efficient Surface to Bulk Catalysis in the Reverse Water-Gas Shift Reaction by the FeO_x/Fe₃C Catalyst

Unraveling the dynamic structural evolution and reaction mechanisms of catalysts from the surface to bulk phase is key to advancing the understanding of catalytic origins. Herein, we report that an in situ formed dynamic FeO_x/Fe₃C heterostructure serves as the catalytically active phase, enabling rapid carbon and oxygen atom exchange with reactants under the reverse water-gas shift (RWGS) reaction. On the disordered FeO_x (1 ≤ x ≤ 1.5) surface, CO₂ is dissociated into gaseous CO and surface O, while partial CO further decomposes into C that infiltrates into the Fe₃C lattice. The C atoms from bulk Fe₃C can combine with the O atoms on FeO_x to form CO, allowing Fe₃C to serve as a reservoir for C atom transfer. Meanwhile, H₂ effectively removes residual surface oxygen to prevent overoxidation. The FeO_x/Fe₃C catalyst, enabled by synergistic surface-to-bulk cycling mechanism, achieves an unprecedented rate of 1.1 × 10^-2 mol/g_cat/s at 600 °C in the RWGS reaction, exceeding all previously reported catalysts. This study reveals mechanistic insight into simultaneous catalysis from the surface to the bulk in heterostructured solid catalysts, offering a new perspective on the origin of the exceptional activity of iron-based catalysts in the RWGS reaction.