Novel bimetallic catalyst supported by red mud for enhanced nitrate reduction

Abstract

The use of red mud as a support material was evaluated in this study to develop a novel bimetallic catalyst for highly reactive and selective nitrate removal from water and wastewater. The catalyst was optimized for the selection of promoter metal (i.e., Sn, Cu, In, and Zn) and then for noble metal (i.e., Pd, Pt, and Au). Sn-Pd-red mud and In-Pd-red mud catalysts achieved a complete nitrate removal. Sn-Pd-red mud showed 5.1 times higher removal kinetics (k = 11.57 × 10−2 min−1) than that of In-Pd-red mud (k = 2.27 × 10−2 min−1). The results from characterization study confirmed that the enhanced nitrate removal kinetics of Sn-Pd-red mud was mainly attributed to 1) its high affinity towards nitrate, 2) low alloying effect of Sn on Pd, 3) high reduction potential of Sn, and 4) high H2 activation by Pd, as compared to those of other red mud supported bimetallic catalysts. We also found that the interaction between CaO and Fe2O3 was the driving force for the enhanced nitrate reduction and high N2 selectivity in this study. A complete nitrate removal with high N2 selectivity (>88%) was preserved during the 11 times of recycling tests with consistent reduction kinetics (k = 10.87 ± 0.48 × 10−2 min−1), indicating that red mud could be an excellent support material for efficient and durable bimetallic catalyst for the enhanced selective nitrate reduction.