Chlorate (ClO3−) is an undesirable byproduct formed at the anode in chloro-alkali process and other electrochemical technologies such as water splitting. ClO3− has also been heavily used in various industrial and agricultural applications, leading to widespread environmental pollution and challenges for water supply. Since ClO3− has negative effects on both human health and manufacturing process, an efficient and robust approach for its removal is of great interest. Catalytic reduction of ClO3− by platinum group metal catalysts and H2 gas allows clean conversion of ClO3− to innocuous Cl− (the only byproduct is H2O). However, practical applications of previously reported catalysts are challenged by (1) limited activity at ambient temperature and pressure, (2) severe inhibition by concentrated salts in the brines.
Prof. Jinyong Liu’s lab at UCR has developed a novel heterogeneous catalyst for aqueous ClO3− reduction. The catalyst contains earth-abundant molybdenum (Mo) and is 55-fold more active than palladium on carbon (Pd/C). Under 1 atm H2 and room temperature, the bimetallic catalyst (MoOx−Pd/C) enables rapid and complete reduction of ClO3− in a wide concentration range (e.g., 1 μM to 1 M) and exhibits strong resistance to concentrate salts such as chloride, sulfate, and bromide at 1 to 5 M. In a batch reactor setup, the catalyst was reused for twenty cycles of 0.18 M ClO3− reduction and no activity loss was observed.
Fig. 1 shows the effect of concentrated salts on the reduction of 1 mM ClO3− by the MoOx-Pd/C catalyst at a loading of 0.2 g/L. The reactions were conducted at 25 oC and under 1 atm H2.
Fig. 2 shows the reduction of 1 M ClO3− in DI water and the treatment of a synthetic chlor-alkali waste brine sample (0.17 M of ClO3− in 3.6 M of NaCl) by 0.5 g/L MoOx-Pd/C.
Fig. 3 shows the profiles of the reduction of 0.18M ClO3− spikes in a multiple-spike reaction series. The decrease of activity was only caused by the gradual build-up of concentrated Cl− (see details in the publication).
The high activity, outstanding stability, and strong resistance to common salts make the MoOx−Pd/C suitable for removing ClO3− and other oxyanions in the brine in the chlor-alkali process and other scenarios such as water purification, wastewater treatment, and waste brine valorization.