Nitrogen gas selectivity enhancement on nitrate denitrification using nanoscale zero-valent iron supported palladium/copper catalysts

• (Cu–Pd)–nFe0 and (Pd–Cu)–nFe0 are effective reductants to selectively reduce NO3− to N2 gas.
• The reduction rate constant was evaluated by a pseudo-second-order reaction model.
• The parametric study shows the synergistic effect on the enhancement of NO3− reduction rate and N2 gas selectivity, but the antagonistic effect on the NH4+ accumulation in the trimetallic system.
• The result appears that combination of Cu (suitable for the reduction of nitrate) and Pd (suitable for the reduction of nitrite) are necessary for the satisfactory reduction of NO3− into N2 gas.

Nanocomposite trimetals, (Cu–Pd)–nFe0 and (Pd–Cu)–nFe0, were used for enhancing both nitrogen gas selectivity and nitrate removal. The initial pH, temperature and initial nitrate concentration were investigated as variable parameters in this study. It was found that the trimetal (Pd–Cu)–nFe0 (10% (Pd–Cu) loading and 2:1 (Pd:Cu) ratio) is promising under the conditions of 50 °C, pH 7 and 100 mg NO3−/L; its largest N2 gas selectivity was 60.5%, and NO3− removal 90%. Based on the kinetic analysis, pseudo-second-order reaction was closely followed under the studied conditions. Higher nitrate removal rate was observed under acidic and high temperature conditions. The activation energy of nitrate reduction over the temperature range of 20–50 °C was 51.0 kJ mol−1.

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