Molybdenum-Catalyzed Perchlorate Reduction: Robustness, Challenges, and Solutions
Changxu Ren, Eric Bi, Jinyu Gao, Jinyong Liu
Abstract
We have recently developed a highly active ligand-enabled (L)Mo–Pd/C catalyst (L = 4,4′-diamino-2,2′-bipyridine) for aqueous perchlorate (ClO4–) reduction with 1 atm H2 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.