Theoretical study on the co-adsorption effect of H atoms on NH3 decomposition over Pt(100) and Pt(111) surfaces

The influence of co-adsorbed hydrogen (H) atoms on the decomposition of ammonia (NH₃) over two representative crystalline facets of platinum catalyst, i.e., Pt(100) and Pt(111), is investigated using density functional theory (DFT) and microkinetic modeling. The results reveal that NH₃ preferentially adsorbs on top sites, with its binding strength decreasing at higher coverages due to intermolecular repulsion. Although NH₃ adsorption is progressively unfavored on both facets with increased coverage by co-adsorbed H atoms, facet-dependent effects are observed: while Pt(100) maintains stable NH₃ decomposition energetics even at high H coverages, Pt(111) shows significant inhibition effect with increased reaction barriers and destabilized intermediates. Microkinetic simulations further confirm that Pt(100) exhibits superior catalytic activity, particularly in N–N coupling and N₂ desorption, compared to Pt(111). These findings highlight the critical role of surface structure and hydrogen coverage in modulating NH₃ decomposition kinetics, providing insights for optimizing Pt-based catalysts in NH₃-based energy systems.