Deciphering Hot-Carrier Effects on Multiple Elementary Steps in Ammonia Decomposition

Abstract Plasmonic photocatalysis can enhance conventional chemical transformations, but macroscale kinetic metrics, such as overall reaction rates and apparent activation barriers, are insufficient to identify the specific elementary steps modulated by hot carriers, limiting precise control over catalytic reactivity and selectivity. Here, we apply a spectrokinetic strategy based on in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to resolve elementary-step energetics in NH3 decomposition over CuRu alloy antenna–reactor catalysts. CuRu and Na-modified CuRu show different relative sensitivities to heating and illumination, providing a paired system for tracking how kinetic control is redistributed under thermal and plasmonic conditions. Temporal in situ DRIFTS and Arrhenius analysis identify site-dependent adsorbed N2 (*N2) intermediates and reveal a sequential migration–desorption pathway for *N2 removal. Thermal kinetic analysis shows that Na enhances thermocatalytic activity, despite strengthening *N2 binding and increasing the *N2 desorption barrier at terrace sites, while DFT calculations suggest that this enhancement is consistent with a reduced interfacial N–N coupling barrier. Under illumination, CuRu exhibits a nearly three-orders-of-magnitude light-specific rate enhancement, accompanied by decreases of 0.75 and 0.28 eV in the activation barriers for terrace *N2 desorption and interfacial *N2 migration, respectively, relative to dark thermal conditions. Comparing CuRu and CuRu–Na shows that illumination affects interfacial *N2 migration more selectively than terrace *N2 desorption, identifying interfacial *N2 removal as a site-sensitive step in plasmon-promoted active-site regeneration. These findings connect plasmonic excitation with site-dependent surface dynamics and elementary-step energetics, providing a framework for understanding how light redirects kinetic control in multistep catalysis.