Mechanism and Mitigation of the Decomposition of an Oxorhenium Complex-Based Heterogeneous Catalyst for Perchlorate Reduction in Water

Jinyong Liu, Xi Chen, Yin Wang, Timothy J. Strathmann, Charles J. Werth

Research output: Contribution to journalArticlepeer-review


A biomimetic heterogeneous catalyst combining palladium nanoparticles and an organic ligand-coordinated oxorhenium complex on activated carbon, Re(hoz)2-Pd/C, was previously developed and shown to reduce aqueous perchlorate (ClO4-) with H2 at a rate ∼100 times faster than the first generation ReOx-Pd/C catalyst prepared from perrhenate (ReO4-). However, the immobilized Re(hoz)2 complex was shown to partially decompose and leach into water as ReO4-, leading to an irreversible loss of catalytic activity. In this work, the stability of the immobilized Re(hoz)2 complex is shown to depend on kinetic competition between three processes: (1) ReV(hoz)2 oxidation by ClO4- and its reduction intermediates ClOx-, (2) ReVII(hoz)2 reduction by Pd-activated hydrogen, and (3) hydrolytic ReVII(hoz)2 decomposition. When ReV(hoz)2 oxidation is faster than ReVII(hoz)2 reduction, the ReVII(hoz)2 concentration builds up and leads to hydrolytic decomposition to ReO4- and free hoz ligand. Rapid ReV(hoz)2 oxidation is mainly promoted by highly reactive ClOx- formed from the reduction of ClO4-. To mitigate Re(hoz)2 decomposition and preserve catalytic activity, ruthenium (Ru) and rhodium (Rh) were evaluated as alternative H2 activators to Pd. Rh showed superior activity for reducing the ClO3- intermediate to Cl-, thereby preventing ClOx- buildup and lowering Re complex decomposition in the Re(hoz)2-Rh/C catalyst. In contrast, Ru showed the lowest ClO3- reduction activity and resulted in the most Re(hoz)2 decomposition among the Re(hoz)2-M/C catalysts. This work highlights the importance of using mechanistic insights from kinetic and spectroscopic tests to rationally design water treatment catalysts for enhanced performance and stability.

Original languageEnglish (US)
Pages (from-to)12932-12940
Number of pages9
JournalEnvironmental Science and Technology
Issue number21
StatePublished - Nov 3 2015

ASJC Scopus subject areas

  • General Chemistry
  • Environmental Chemistry


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