Activated carbon supported metal catalysts for reduction of nitrate in water with high selectivity towards N2

The catalytic removal of nitrate in water with hydrogen was investigated by using different activated carbon-supported metal catalysts. A commercial activated carbon (CAC) and one prepared by chemical activation of grape seeds with phosphoric acid (GS) were evaluated for the preparation of bimetallic catalysts (Pd-Cu, Pd-Sn and Pd-In). The support plays an important role in the catalytic performances for nitrate removal, affecting both activity and selectivity. Pd-Cu catalyst supported on GS showed the highest nitrate removal activity and nitrite was not found as by-product. The acidity of the reaction medium is associated with this behavior, attributing this effect to the chemical composition of the catalyst support. Control of pH through CO2 addition to the reaction medium was beneficial in the case of the Pd-Cu catalyst prepared with CAC. However, no significant influence was observed in the case of the GS-supported catalyst. The concentration of promoting metal affects more strongly the catalyst performance than that of Pd. Low Cu contents (0.5 and 1.5 wt.%) within the range tested (0.5-5 wt.%) led to the highest selectivity towards the undesired ammonium ion. The catalysts supported on GS with 2.5% Cu and 5% Pd allowed achieving the European Standards for drinking water when a 100 mg/L nitrate starting solution was treated, in terms of nitrate, nitrite and ammonium concentrations. The Pd-based bimetallic catalysts containing Sn and In as promoting metal showed a lower catalytic activity and significantly higher selectivity towards ammonium. (C) 2013 Elsevier B.V. All rights reserved.