Supporting palladium metal on gold nanoparticles improves its catalysis for nitrite reduction

Abstract

Nitrate (NO3(-)) and nitrite (NO2(-)) anions are often found in groundwater and surface water as contaminants globally, especially in agricultural areas due to nitrate-rich fertilizer use. One popular approach to studying the removal of nitrite/nitrate from water has been their degradation to dinitrogen via Pd-based reduction catalysis. However, little progress has been made towards understanding how the catalyst structure can improve activity. Focusing on the catalytic reduction of nitrite in this study, we report that Au NPs supporting Pd metal ("Pd-on-Au NPs") show catalytic activity that varies with volcano-shape dependence on Pd surface coverage. At room temperature, in CO2-buffered water, and under H2 headspace, the NPs were maximally active at a Pd surface coverage of 80%, with a first-order rate constant (k(cat) = 576 L g(Pd)(-1) min(-1)) that was 15x and 7.5x higher than monometallic Pd NPs (~4 nm; 40 L g(Pd)(-1) min(-1)) and Pd/Al2O3 (1 wt% Pd; 76 L g(Pd)(-1) min(-1)), respectively. Accounting only for surface Pd atoms, these NPs (576 L g(surface-Pd)(-1) min(-1)) were 3.6x and 1.6x higher than monometallic Pd NPs (160 L g(surface-Pd)(-1) min(-1)) and Pd/Al2O3 (361 L g(surface-Pd)(-1) min(-1)). These NPs retained ~98% of catalytic activity at a chloride concentration of 1 mM, whereas Pd/Al2O3 lost ~50%. The Pd-on-Au nanostructure is a promising approach to improve the catalytic reduction process for nitrite and, with further development, also for nitrate anions.

Volcano-shape glycerol oxidation activity of palladium-decorated gold nanoparticles

“…It was not known how the oxidation states of Pd-on-Au would be affected by the harsher conditions of glycerol oxidation (60 C, O 2 atmosphere, and pH $ 13.5) compared to those of TCE HDC (room temperature, H 2 atmosphere, near-neutral pH). [36][37][38][39][40][41][42] We thus performed ex situ XANES characterization on 4 samples (Au NPs, Pd NPs, and the two Pd-on-Au NP compositions) under 3 conditions: as-prepared, before the oxidation reaction, and aer the oxidation reaction.…”

Pressure-driven membrane and ion exchange hybrid system for the treatment of wastewater containing sulfite and nitrite

“…However, the concentration of nitrite ions in the RO permeate remained higher than the regulated level (1.0 mg N/L or 4.9 mg NaNO À 2 /L) [24] set by the United States Environmental Protection Agency (US EPA). Therefore, IX was used to further remove nitrite.…”

Catalytic reduction of nitrite in water over ceria- and ceria–zirconia-supported Pd catalysts

“…The Hörold group reported that the ammonium formation was favored in the high pH conditions [2]. In order to lower pH values, Qian et al used CO 2 gas as a pH buffer for the nitrite reduction [46]. Accordingly, we tested the PCZ1 catalyst (which had the best activity) under constant H 2 flow rate of 90 mL/min and varied CO 2 of 10, 30, 60 and 90 mL/min.…”