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.