Molybdenum-Catalyzed Perchlorate Reduction: Robustness, Challenges, and Solutions

We have recently developed a highly active ligandenabled (L)Mo-Pd/C catalyst (L = 4,4 '-diamino-2,2 '-bipyridine) for aqueous perchlorate (ClO4-) reduction with 1 atm H-2 at room temperature. This study reports on a series of satisfactory properties of this catalyst closely relevant to ClO4- treatment in waste brines resulting from ion-exchange resin regeneration. In the presence of concentrated salts and humic acid, the catalyst experienced limited inhibition but completed ClO4- reduction in a few hours with an adjustable loading between 0.2 and 2 g/L. The catalyst was not deactivated by the high oxidative stress from multiple spikes of 100 mM ClO4-. The challenge of deactivation by nitrate was solved by pretreating the brine with In-Pd/Al2O3. The loss of activity upon ligand hydrogenation was overcome by regenerating the Pd/C at pH 12. We also optimized the catalyst formulation and saved 70% of Pd without sacrificing the activity. The substantially enhanced performance and lowered adverse environmental impacts of (L)Mo-Pd/C make the catalytic treatment competitive to microbial reactors for ClO4- reduction. We showcase the power of coordination chemistry in environmental technology innovation and expect this catalyst to promote the reuse of ClO4--selective resins for sustainable water treatment.