The origin of highly efficient and selective activated carbon supported bimetallic Fe@Cu composite for Fe(II)EDTA-NO reduction in Fe(II)EDTA complexation denitrification process

Abstract

Fe(II)EDTA complexing absorption is a promising technology for nitric oxide removal; however, inefficient and slow Fe(II)EDTA regeneration from Fe(II)EDTA-NO reduction and undesirable NH4+ as the major N-containing product are still challenges that should be resolved. This study investigated the performance, kinetics, and product selectivity of Fe(II)EDTA-NO reduction by activated carbon supported bimetallic Fe@Cu composite (AC-Fe@Cu) and unraveled the origin of highly efficient and selective AC-Fe@Cu for Fe(II)EDTA-NO reduction. The reduction efficiency reaches 95.34 % in 30 min, accompanied by 86.78 % N2 selectivity, outperforming most of the reduction systems reported previously. AC-Fe@Cu is resilient at wide pH (3–8), temperature (20–50 °C), and O2 concentration ranges (0–10 %) and maintains high efficiency (76.23 %) after three successive cycles (3 h). Simultaneous reduction of Fe(III)EDTA and Fe(II)EDTA-NO indicates that Fe(II)EDTA-NO reduction is the rate-determining step in the Fe(II)EDTA regeneration process. The bimetal configuration and atomic ratio mediate the reduction efficiency, rate, and N2 selectivity. Unique AC@Fe@Cu structure and optimal atomic ratio of Fe to Cu (1:1) increase the dispersity and provide space proximity and abundant interfaces, which create numerous iron–carbon and iron–copper galvanic cells and promote two-way electron transmission. Fast electron transfer and nascent hydrogen formation contribute to efficient, rapid, and selective Fe(II)EDTA-NO reduction. The maximization of the roles of Cu as stabilizer and active sites for selective N2 formation also contributes. This study sheds light on reduction system design for Fe(II)EDTA regeneration.