Hot electron-driven nitrate-to-ammonia conversion on nanocatalysts: insights from quantum dynamics simulations

Abstract

Photocatalytic nitrate (NO₃) to ammonia reduction offers a sustainable alternative to conventional energy-intensive routes, yet poor selectivity and sluggish multielectron kinetics remain significant roadblocks to the technological adoption of this approach. Here, we show that metal-rich cadmium selenide (CdSe) quantum dots (QDs) serve as efficient hot carrier photocatalysts, enabling ultrafast NO₃⁻ reduction to ammonia. The ab initio quantum molecular dynamics simulations track the ultrafast hot electron (HE) transfer at the QD/NO₃ interface. The lowest unoccupied molecular orbital (LUMO) of the reactant NO₃ acts as the primary electron acceptor, accumulating ∼70% of the generated HE population. The impulsive two-state model explores the reaction dynamics following the photoexcitation of the LUMO, capturing ultrafast bond rearrangement processes. The presence of undercoordinated surface Cd centers excites antisymmetric vibrational modes, facilitating NO₃⁻ dissociation to NO₂⁻ + O*. Subsequent ultrafast reduction steps then convert NO₂⁻ to NO and ultimately exothermically reduce it to the final product, NH₃. These findings depict a detailed atomistic perspective on hot-carrier-driven NO₃ reduction to ammonia and suggest design principles for engineering QD-based photocatalysts with enhanced selectivity and efficiency.