Abstract
In this study, we investigated catalytic nitrate removal using nanoscale zerovalent iron (NZVI) supported Cu-Pd bimetallic catalyst (Cu-Pd/NZVI) in a continuous reactor system. Control experiments showed that Cu, Pd, and a proper supply of H-2 are essential for relatively sustainable nitrate (30 mg/L NO3--N) reduction in continuous mode. When we optimized operational parameters to enhance removal efficiency and N-2, selectivity, we finally achieved complete nitrate removal with 48% N-2 selectivity at 9 h. During a longevity test (200 h reaction), excellent removal was observed (>91% in 24 h) with 42-60% N-2 selectivity. However, removal gradually decreased to 13% in 200 h with increasing nitrite production. X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy analysis revealed that both the support (NZVI) and the Cu(0) oxidized after continuous denitrification. This indicated that loss of NZVI reductive capacity and the oxidation of Cu(0) to Cu(I) and Cu(II) deactivated nitrate removal during the continuous nitrate reduction by Cu-Pd/NZVI.