Synergistic integration of catalysis and ion-exchange for highly selective reduction of nitrate into N2

• We demonstrate an integrated denitrification technology combining catalysis and ion-exchange.
• PdCu supported on ion-exchange resin was used as a bifunctional material.
• After the resin selectively captures NO3−, the concentrated NO3− is reduced by the supported PdCu.
• In the presence of H2/CO2 mixed gas, 100% catalytic selectivity to N2 was achieved.
• The ion-exchange/catalytic regeneration was repeated five times without a loss of a performance.

An integrated process synergistically combining the advantages of catalysis and ion-exchange is demonstrated for the selective and complete degradation of NO3− from contaminated water. To realize this process, PdCu catalysts were supported on an ion-exchange resin. The functional resin captures NO3− in an ion-exchange mode, whereas the concentrated NO3− in the resin is fully reduced by the supported PdCu in a catalytic regeneration mode. The complete conversion of the captured NO3− indicates that the solid-state diffusion of NO3− within the resin is possible through consecutive ion-hopping. Catalytic resin regeneration under H2/CO2 (1/1, v/v) was found to reduce NO3− to N2 selectively without the formation of the toxic byproduct NH4+. The complete suppression of the NH4+ formation (∼100% N2 selectivity) has never been reported previously. It is well known that the accumulation of OH− ions generated during the NO3− reduction significantly enhances the formation of NH4+. We propose that OH− ions generated on the catalyst surface are rapidly captured by the ion-exchange sites of the resin, thus minimizing the detrimental interaction between OH− and the catalyst surface. The ion-exchange/catalytic regeneration cycle could be repeated up to five times without a loss of the NO3− ion-exchange capacity or catalytic regenerability.

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