Abstract:
The presence of various oxyanions in the groundwater could be the main challenge for the successive application
of Cu–Pd-hematite bimetallic catalyst to aqueous NO3
− reduction due to the inhibition of its catalytic reactivity
and alteration of product selectivity. The batch experiments showed that the reduction kinetics of NO3
− was
strongly suppressed by ClO4
− , PO4
3− , BrO3
− and SO3
2− at low concentrations (>5 mg/L) and HCO3
− , CO3
2− ,
SO4
2− and Cl− at high concentrations (20–500 mg/L). The presence of anions significantly changing the end product selectivities influenced high N2 selectivity. The selectivity toward N2 increased from 55% to 60%,
60%, and 70% as the concentrations of PO4
3− , SO3
2− , and SO4
2− increased, respectively. It decreased from 55%
to 35% in the presence of HCO3
− and CO3
2− in their concentration range of 0–500 mg/L. The production of NO2
−
was generally not detected, while the formation of NH4
+ was observed as the second by-product. It was found
that the presence of oxyanions in the NO3
− reduction influenced the reactivity and selectivity of bimetallic
catalysts by i) competing for active sites (PO4
3− , SO3
2− , and BrO3
− cases) due to their similar structure, ii)
blockage of the promoter and/or noble metal (HCO3
− , CO3
2− , SO4
2− , Cl− and ClO4
− cases), and iii) interaction
with the support surface (PO4
3− case). The results can provide a new insight for the successful application of
catalytic NO3
− reduction technology with high N2 selectivity to the contaminated groundwater system.