Applicability of a catalytic reduction method using a palladium–copper catalyst and hydrazine for the denitration of a highly concentrated nitrate salt solution

Figures & data

Figure 1. An apparatus for denitration experiment. (a) A four necked separable flask, (b) a water bath, (c) a underwater magnetic stirrer, (d) a measuring cylinder, (e) a peristaltic pump, (f) a tygon tube, (g) a condenser tube, and (h) a recirculating cooler.

Table 1. Calculated and found ratios for the Pd and Cu supported on carbon powder.

	Pd (mmol g^−1)	Cu (mmol g^−1)
Calculated	0.47	0.39
Found	0.46	0.37

Figure 2. XRD patterns for the carbon powders 0.47 Pd–x Cu/C (x = 0−0.39) and y Pd–0.39 Cu/C (y = 0−0.47). (a) Carbon powder, mole fraction of Cu/(Pd + Cu) = (b) 0, (c) 0.14, (d) 0.25, (e) 0.40, (f) 0.46, (g) 0.51, (h) 0.68, (i) 0.81, and (j) 1.

Figure 3. Concentrations of NO₃ ⁻, NO₂ ⁻, and N₂H₄ in suspension as a function of time. Reaction solution: 100 mL of 5 mol L⁻¹ NaNO₃, catalyst: 2 g of 0.47 Pd–0.31 Cu/C, reductant: 40 mL of N₂H₄ · H₂O, drop rate of N₂H₄ · H₂O: 80 mL h⁻¹, temperature: 333 K. •: NO₃ ⁻, ○: NO₂ ⁻, □: N₂H₄.

Figure 4. Reaction rates of NO₃ ⁻ and NO₂ ⁻ using several catalysts with different Cu fractions. Reaction solution: both 100 mL of 0.5 mol L⁻¹ NaNO₃ and NaNO₂, catalyst: 0.2 g of 0.47 Pd–x Cu/C (x = 0−0.39) or y Pd–0.39 Cu/C (y = 0−0.47), reductant: 4 mL of N₂H₄ · H₂O, temperature: 333 K. •: NO₃ ⁻, ○: NO₂ ⁻.

Table 2. Comparison of the reaction rate of NO₂ ⁻ using H₂ and N₂H₄.

Reductant	Reaction rates (h^−1)
	Pd/C	Pd–Cu/C	Cu/C
H2 ^a	1.8	1.7	–
N2H4 ^b	26	106	–
Notes: ^a100 mL of 5 × 10^−3 mol L^−1 NaNO2; ^b100 mL of 0.5 mol L^−1 NaNO2. Reductant: 30 mL min^−1 of H2, 4 mL of N2H4 · H2O, temperature: 333 K. “–” means that reaction was not observed.