The reaction mechanism of*CHx formation in Fischer-Tropsch synthesis on various FeRh nanoclusters is studied using DFT calculations. We find that the energy barrier of*CH2 formation from hydrogen-assisted*CH2O dissociation can be directly modulated using the Fe/Rh composition ratio. Thermodynamic investigations and the natural bond orbital (NBO) analysis indicate that the barrier dropping of C-O bond scission in*CH2O can be ascribed to the interaction between the Fe and the O atoms. In particular, the*CH2 formation can be selectively stabilized with respect to the*CH3O formation using a local tri-Fe configuration on the FeRh nanocluster when the Fe ratio exceeds 50%. An optimal barrier may be achieved by carefully balancing the number of Rh and Fe atoms in the local configuration of the active site to stabilize both ends of the intermediates.
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