Bypassing Hydrogenation Pathway for Sustainable Nitrate Water Remediation via Direct N─N Coupling

Catalytic nitrate (NO₃ ^-) reduction (CNR) to dinitrogen (N₂) offers an efficient strategy for remediating nitrogen pollution but is constrained by preferred ammonia (NH₃) formation. This selectivity challenge arises because hydrogen atom (H*)-mediated pathway inherently favors N─H coupling over the desired N─N coupling. Here, we report a formic acid (HCOOH)-driven proton-coupled electron transfer (PCET) pathway on a precisely engineered Sn₃/Pd catalyst. The catalyst design features a synergistic bimetallic interface where Pd sites facilitate HCOOH activation while triangular Sn₃ ensembles selectively adsorb NO₃ ^-. This direct PCET from HCOOH to NO₃ ^- achieved a remarkable 96.5% NO₃ ^- removal and 97.4% N₂ selectivity at environmentally relevant concentrations (100 mg-N/L). Operando mass spectrometry and density functional theory (DFT) calculations reveal that Sn₃ ensembles thermodynamically favored N─N coupling while also acting as a steric barrier that kinetically impedes H* migration to adsorbed N* intermediates, effectively suppressing NH₃ formation. Furthermore, by integrating the CNR process with electro-synthesized HCOOH, we demonstrated a synergistic technology that slashed the carbon footprint of wastewater treatment by 43.3%, decreasing from 33.50  kg CO₂-eq t^-1 to 19.01  kg  CO₂-eq t^-1. Our work establishes atomic ensemble engineering as a powerful strategy to steer catalytic pathway through PCET, offering a viable solution for sustainable NO₃ ^- removal.