Highly fast and selective removal of nitrate in groundwater by bimetallic catalysts supported by fly ash-derived zeolite Na-X

A novel and sustainable Pd–Sn bimetallic catalyst supported by fly ash-derived zeolite Na-X (Zeolite-XF) was developed for highly reactive and N2-selective reduction of nitrate in water. The surface characteristics of Zeolite-XF and Pd–Sn/Zeolite-XF were identified via various surface analyses, which showed formation of zeolite Na-X crystals with high purity and uniform dispersion of Pd and Sn nanoparticles on the surfaces of Pd–Sn/Zeolite-XF. Pd–Sn/Zeolite-XF showed a 43.1 × 10−3 s−1 turnover frequency (TOF) with almost 90% N2 selectivity under optimal conditions, which is 4–92 times higher than those of previously reported Pd based bimetallic catalysts. The great catalytic activity was elucidated by XPS and H2-pulse chemisorption analysis, demonstrating that Zeolite-XF enhanced metal dispersion and increased the active metallic sites of Pd and Sn nanoparticles. Furthermore, the optimized Pd–Sn/Zeolite-XF catalyst was tested for reduction of nitrate in real groundwater, which showed the complete removal with 94% N2 selectivity. The experimental results obtained from this study can provide a new insight that discarded solid waste can be converted to value-added environmental materials for synthesis of highly active catalysts, which surpass other freshly synthesized and commercially produced materials.