Hydrogen Radical‐Mediated Nitric Oxide Reduction to Ammonia Over Synergistic Pd ⁰ /Pd ²⁺ Dual Sites

Abstract

ABSTRACT The photocatalytic nitric oxide reduction reaction (NORR) to NH 3 offers a promising route for ammonia (NH 3 ) synthesis, addressing environmental issues and mitigating the carbon footprint associated with the energy‐intensive Haber‐Bosch process. However, conventional sluggish multi‐proton‐coupled electron transfer (PCET) and poor regulation of valence states at active sites hinder the efficiency of NORR. Herein, we propose a hydrogenation pathway driven by hydrogen radicals ( • H) utilizing ethylene glycol (EG) as a hydrogen donor, which effectively bypasses the limitations of the conventional PCET process. By precisely modulating the valence states of Pd cocatalysts, we construct synergistic Pd 0 /Pd 2+ dual active sites, where Pd 2+ sites facilitate the dissociation of C‐H bonds from EG to supply adsorbed H species (*H), which are subsequently activated into highly reactive • H by photogenerated electrons at Pd 0 sites. This synergistic effect of Pd 0 /Pd 2+ guarantees a steady flux of • H for deep NORR. Optimizing the Pd 0 /Pd 2+ ratio to unity (Pd 1.0 /TiO 2 ‐50) enabled a superior NH 3 yield rate of 31.61 ± 1.61 mmol∙g cat −1 ∙h −1 with high NO conversion (91.54% ± 1.82%) and NH 3 selectivity (90.14% ± 1.38%) in a single pass flow. Comprehensive in situ characterizations elucidate the causality between Pd valence states and radical generation, offering a new paradigm for designing and understanding the radical‐mediated chemistry.