Surface-Plasmon-Induced Ammonia Decomposition on Copper: Excited-State Reaction Pathways Revealed by Embedded Correlated Wavefunction Theory

Ammonia is a promising hydrogen storage medium; however, its decomposition via conventional thermal catalysis requires a significant amount of thermal energy input in order to overcome the reaction barriers. Here, we use embedded correlated wavefunction (ECW) theory to quantify reaction pathways and energetics for ammonia decomposition (N-H bond dissociation and N₂ and H₂ associative desorption) on copper (Cu) nanoparticles using a Cu (111) surface model. We predict that surface plasmon excitations will be able to facilitate ammonia decomposition by substantially reducing the effective barriers along excited-state pathways. We estimate the reductions in reaction barriers for breaking the first N-H bond and for recombinative desorption of surface-bound nitrogen and hydrogen atoms to be approximately 1.7, 0.8, and 0.5 eV, respectively. Further, by using the experimental N₂ desorption barrier as a reference, we compare the accuracy of various theoretical methods, including plane-wave Kohn-Sham density functional theory calculations with commonly used exchange-correlation functionals, embedded complete active space second-order perturbation theory, and embedded multiconfiguration pair-density functional theory. This work offers further confirmation that the ECW theoretical framework is the most robust for treating highly correlated local electronic structures of solids.