The heterogeneous bimetallic catalyst, Re(hoz)2-Pd/C, has excellent activity to reduce perchlorate (ClO4-) in water into Cl- using H2 under ambient temperature and pressure. The traditional synthetic method for the catalyst precursor, Re(O)(hoz)2Cl complex, produced two isomers. The N,N-trans isomer shows 16 times higher ClO4- reduction activity than the N,N-cis isomer via different reaction pathways. The key factors determining the isomer formation are identified, and strategies for controlled synthesis of each isomer are established. By immobilizing the N,N-trans Re(O)(hoz)2Cl complex into Pd/C by a convenient aqueous deposition method, the Re(hoz)2-Pd/C catalyst shows two orders-of-magnitude higher activity than the previous ReOx-Pd/C catalyst prepared from perrhenate (ReO4-). The ClO4- reduction kinetics and ReO4- leaching from Re(hoz)2-Pd/C under a series of conditions (e.g., different ClO4- concentrations, pH values, anions and cations) are measured. The transformation between ReI, ReIII, ReV and ReVII under various conditions is characterized by X-ray photoelectron spectroscopy. Experiments in homogeneous phase are also conducted to improve the understanding of mechanisms at the heterogeneous interface. Finally, an overall mechanistic scheme on reaction pathway and Re transformation is proposed for the Re(hoz)2-Pd/C catalyst toward ClO4- reduction in water.

Ligand-enhanced Re-Pd/C catalyst for perchlorate reduction in water: Preparation, characterization, structure-activity relationship, and reaction mechanisms

246th National Meeting (2013)

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