Performance and mechanism of chelating resin (TP-207) supported Pd/Cu bimetallic nanoparticles in selective reduction of nitrate by using ZVI (zero valent iron) as reductant

Abstract

• Novel Pd/Cu-resin catalyst was applied for denitrification by using ZVI as reducing agent. • High N 2 selectivity (>90%) in final products of nitrate reduction were obtained under neutral condition. • High N 2 selectivity may be brought by the slow rate of nitrate reduction. • ZVI, Pd/Cu-resin, and the neutral conditions with high N/H ratio resulted in low ammonia production and high N 2 selectivity. In the present study, a Pd/Cu bimetallic catalyst supported on a chelating resin (TP207) was prepared in order to selectively reduce nitrate to N 2 with ZVI (zero valent iron) as a reductant. The effects of Pd/Cu mass ratio, temperature, and initial solution pH on the removal of nitrate and TN were then examined. The highest nitrate (63.2%) removal was obtained under neutral conditions at a ratio of Pd/Cu 2:1, in which 57.8% of TN was removed and N 2 accounted for more than 90% of the final products. Additional ammonia (30–40%) were formed when the reaction was conducted at a higher temperature (313 K) compared to when performed at 303 K. The mechanism study for nitrate reduction indicated that this catalyst could broaden the suitable pH range and improve the selectivity of N 2 without the generation of other intermediate compounds or by-products in comparison to ZVI and its combination with a non-supported Pd/Cu catalyst. The slow rate of ZVI corrosion, high Fe(Ⅱ) proportion in corrosion products and high N/H ratio at neutral pH conditions may serve as reasons for the high N 2 selectivity. The chelating resin also played a key role via its load capacity and dispersion ability to Pd/Cu particles in enhancing N 2 selectivity. Accordingly, the proposed method may have great potential application for nitrate reduction to N 2 , which warrants further study.