Amorphous Pd nanoparticles inside ethylenediamine-based nanocomposite for high N₂-selectivity of nitrate reduction

Catalytic reduction of nitrate to dinitrogen (N₂) by noble metals stands as a feasible and promising manner to address the biological and environmental issues associated with nitrate pollution; however, nitrate reduction under single noble-metal catalyzation remains substantially stuck because of the low adsorption enthalpy of noble metal toward nitrate. Tailoring the formation (crystal structure and particle size) of catalytical metal particles, coupled with a more direct electron donating pattern, provides a potential solution for the main challenge in reduction efficiency and selectivity. In this study, we assembled a Pd-based nanocomposite (Pda@EC) by subtly regulating the embedded Pd nanoparticles inside a porous substrate self-sufficient in electron donator (i.e., ethylenediamine group, EDA). Without any provision of reductant, the resultant single-metal catalyst demonstrated excellent nitrate catalytic reduction with over 95 % of N₂ reduction selectivity within very broad pH range (3-11), whereas its unregulated counterpart (crystal Pd nanocomposite, Pdc@EC) is incapable of efficient nitrate reduction under otherwise identical conditions. The activated hydrogen (H*), which was exclusively yielded under the catalyzation of the amorphous Pd nanoparticles for the electron donating EDA, was confirmed as the primary active species, and the high N₂ selectivity is attributed to the cooperation between EDA and Pd nanoparticles. More promisingly, the exhausted Pd_a@EC is amenable to effective regeneration with mild NaOH (elution) and NaBH₄ (restoration) treatment. This work provides an effective strategy for selectively reducing nitrate under monometallic catalyzation by subtly regulating the crystal structure of Pd nanoparticles in endogenous electron-donating environment.