Possible Strong Promotional Effect of Al2O3 on Fe Catalysts for Ammonia Synthesis via Fe/γ-Al2O3

Al2O3 is a critical component in Fe-based catalysts for ammonia synthesis, yet its precise promotional role remains elusive. In this work, we employ density functional theory (DFT) and molecular dynamics (MD) simulations to investigate the catalytic behavior of Fe surfaces supported on γ-Al2O3, the most common phase of Al2O3 used as a support. A series of Fe(110)/γ-Al2O3 models with varying Fe layer thicknesses are constructed, in which the Fe(110) facet is typically the least active among Fe surfaces. Reaction energies and activation barriers are computed for each system, followed by microkinetic simulations based on the calculated energetics. The results reveal a pronounced promotional effect of γ-Al2O3: Its interaction with Fe(110) significantly lowers the barrier for N2 dissociative adsorption, elevating the predicted catalytic activity to a level comparable with that of Fe(111), the most active Fe surface. Structural analysis further shows that monolayer Fe(110)/γ-Al2O3 closely resembles the geometry of stepped Fe surfaces. As the number of Fe layers increases, the structural distortion induced by γ-Al2O3 diminishes, and the system gradually reverts to the characteristics of pristine Fe(110).