A novel process for nitrate reduction in water using bimetallic Pd-Cu catalysts supported on ion exchange resin

In this work, a Pd-Cu catalyst supported on a macroporous anion exchange resin was used in two novel processes to treat water contaminated with nitrates. The catalytic performance was evaluated in a continuous fixed bed reactor. The process (Reaction + Ion Exchange) - Regeneration, named RIE-R, has two steps: 1-reaction and ion exchange (RIE); 2-Regeneration (R). It was found that a hydrogen flow rate increase does not affect the nitrate removal efficiency during the RIE step, while the selectivity to nitrogen decreased. The presence of competing ions (sulphate, bicarbonate, chlorides) led to a decrease in the nitrate removal efficiency. In any case, the water obtained in the process meets the limits established by the World Health Organization. During the regeneration step, carried out by bubbling hydrogen to the catalytic bed, 100% of nitrates present in the resin at the end of the RIE cycle were eliminated. The other process, named IE-R, has a first step in which only ion exchange of nitrates occurs, and a second one during which the catalyst is regenerated. This process has worse performance compared to the RIE-R. Only 36.7% of the nitrates present in the resin at the beginning of the regeneration were eliminated. The catalyst was characterized by CO chemisorption, SEM, EPMA, TEM, and XRD. Pd migration towards the external surface occurs during the reaction, and also a decreased in dispersion takes place, leading to a small decrease in activity detected in consecutive reaction-regeneration cycles. A regeneration mechanism is presented. (C) 2017 Elsevier Ltd. All rights reserved.