Pd-Cu Supported on Anionic Polymers - Promising Catalysts for Removal of Nitrates from Drinking Water

Abstract

Removal of nitrates from drinking water by catalytic hydrogenation over polymer supported Pd-Cu catalysts was studied. Precursors of the catalysts were prepared by ion exchange using microporous polymer cation-exchange resin Dowex 50 W X 4 in acid form and acetone-water solution of Pd and Cu acetates. The metals (approximately 2 and 0.5 wt.% of Pd and Cu, respectively) were reduced with NaBH4 in ethanol at room temperature or with H2 in MeOH at 50 °C and 1 MPa. Catalysts made it possible to reduce nitrate content in water from 100 mg/l to less than 50 mg/l after 4 h of batch treatment with hydrogen-nitrogen mixture (43 vol.% H2) at ambient temperature and atmospheric pressure under vigorous stirring of the reaction mixture. The importance of acid sites of the catalyst for the selective hydrogenation of nitrates to nitrogen was demonstrated by a higher overall selectivity (about 60 mole %) obtained on catalysts containing acid sites than on catalysts without acid sites (about 20 mole %). Catalysts bearing acid sites are promising candidates for removal of nitrates, formed ammonia, as well as other cations because of parallel acting as catalysts and cation exchangers. The used catalysts were regenerated with a low concentrated mineral acid.