Hot Electron-Driven Nitrate-to-Ammonia Conversion On Nanocatalyst: Insights from Quantum Dynamics Simulations

Photocatalytic NO3⁻ reduction to NH3 offers a sustainable alternative to established energy-intensive conversion methods but is hindered by poor selectivity and sluggish multi-electron kinetics. Using integrated quantum mechanical simulations, we reveal that metal-rich CdSe quantum dots (QDs) exhibit unusual hot electron (HE)-mediated photocatalytic activity, facilitating ultrafast nitrate (NO3⁻) reduction under ambient conditions. The non-adiabatic molecular dynamics track the ultrafast HE transfer from QD to the lowest unoccupied molecular orbital of NO3, activating its subsequent reduction. The impulsive two-state model captures the real-time HE-mediated N-O bond breaking that results in NO3– to NO2– reduction. The atomistic details emphasize the pivotal role of undercoordinated surface Cd centers in strongly adsorbing and further selectively exciting antisymmetric vibrational modes of the reactant, initiating the photochemical conversion. Our simulations further depict the photo-induced NO2⁻ dissociation to NO, which can desorb and reabsorb on suitable catalytic sites. The computed Gibbs free energy changes illustrate the multistep NO-to-NH3 conversion and facile product desorption via thermodynamically favored successive hydrogenation at the nitrogen center. These in-depth mechanistic findings propose several design principles for engineering QD-based photocatalysts that harvest HEs to boost a wide range of photochemical processes with unprecedented selectivity and efficiency.