Effect of water composition on catalytic reduction of nitrate

Abstract

This work studies catalytic reduction of nitrate with bimetallic catalysts supported on γ-alumina (Pd-Sn/Al2O3 and Pd-In/Al2O3). Pd-Sn/Al2O3 yielded higher NO3− conversion and selectivity towards N2 than Pd-In/Al2O3 in synthetic water (deionized water with 100 mg/L NO3−). The Pd-Sn/Al2O3 catalyst showed highly stable behaviour, without signs of deactivation upon ten consecutive runs of 6 h each, where almost equal low selectivity to NH4+ (absence of NO2−) was maintained at high nearly constant nitrate conversion (≈ 90%). The presence of anions (Cl−, SO42− and HCO3−) in the reaction medium decreased NO3− conversion and the selectivity towards N2. Chloride showed a moderately negative effect at relatively low concentration. The effect of SO42− and HCO3− was more pronounced, being the second the most detrimental to the catalytic activity. The selectivity towards N2 was also negatively affected by the presence of those anions following the sequence HCO3− > SO42− > Cl−. However, the joint presence of Cl− or SO42− with HCO3− reduced the negative effect of the latter. The Pd-Sn/Al2O3 catalyst also showed high activity in NO3− reduction from drinking waters of weak mineralization, with a slightly increase of the selectivity towards NH4+ with respect to the obtained in deionized water with NO3− as the only anion.