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

Abstract

In this work, a Pd-Cu catalyst supported on a macroporous anionexchange resin was used in two novel processes to treat watercontaminated with nitrates. The catalytic performance was evaluated in acontinuous 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 rateincrease does not affect the nitrate conversion during the RIE step,while the selectivity to nitrogen decreased. The presence of competingions (sulphate, bicarbonate, chlorides) led to a decrease in the nitrateconversion. In any case, the water obtained in the process meets thelimits established by the World Health Organization. During theregeneration step, carried out just by bubbling hydrogen to the catalyticbed, 100% of nitrates present in the resin at the end of the RIE cyclewere eliminated.The other process, named IE-R, has a first step in which only ionexchange of nitrates occurs, and a second one during which the catalystis 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 theregeneration were eliminated.The catalyst was characterized by CO chemisorption, SEM, EPMA, TEM, andXRD. Pd migration towards the external surface occurs during thereaction, and also a decreased in dispersion takes place. This has littleeffect on the activity for nitrate reduction.A regeneration mechanism is presented to explain the experimentalobservations.