Synergistic integration of catalysis and ion-exchange for highly selective reduction of nitrate into N-2

Abstract

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 H-2/CO2 (1/1, v/v) was found to reduce NO3- to N-2 selectively without the formation of the toxic byproduct NH4+. The complete suppression of the NH4+ formation (similar to 100% N-2 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.