Enhancement of Pd-based catalysts for the removal of nitrite and nitrate from water

Mono- and bimetallic catalysts have been evaluated in the catalytic reduction of NO₂⁻ and NO₃⁻. The activity and selectivity of the catalysts based on Pd, Pd-In and Pd-Sn supported on different materials such as basic Al₂O₃, SiO₂ and SnO₂ have been evaluated under mild operation conditions (25 °C, 1 atm). NO₂⁻ hydrogenation was efficiently achieved with monometallic Pd catalyst supported on SnO₂ and the bimetallic Pd-In catalysts supported on Al₂O₃ and SiO₂ which led to the highest NO₂⁻ conversion (80%). Pd/SnO₂ and bimetallic Pd-In supported catalysts completely transformed NO₃⁻ while Pd-Sn catalyst showed a lower activity. Initial rates between 0.5 and 2.6 mmol·min⁻¹·g_Pd⁻¹ were obtained for NO₃⁻ reduction. The lowest selectivity to NH₄⁺ was observed with the Pd-In/Al₂O₃ catalyst, which also showed a high stability in long-term experiments. The operation at low relative H₂ fractions in the gas feed greatly diminishes the selectivity to NH₄⁺, reaching concentrations below the maximum concentration allowed in drinking water (0.5 mg/L).