A New Bioinspired Perchlorate Reduction Catalyst with Significantly Enhanced Stability via Rational Tuning of Rhenium Coordination Chemistry and Heterogeneous Reaction Pathway

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• 作者：Jinyong Liu ; Mengwei Han ; Dimao Wu ; Xi Chen ; Jong Kwon Choe ; Charles J. Werth ; Timothy J. Strathmann
• 刊名：Environmental Science & Technology
• 出版年：2016
• 出版时间：June 7, 2016
• 年：2016
• 卷：50
• 期：11
• 页码：5874-5881
• 全文大小：502K
• 年卷期：0
• ISSN：1520-5851

文摘

Rapid reduction of aqueous ClO₄^– to Cl^– by H₂ has been realized by a heterogeneous Re(hoz)₂–Pd/C catalyst integrating Re(O)(hoz)₂Cl complex (hoz = oxazolinyl-phenolato bidentate ligand) and Pd nanoparticles on carbon support, but ClO_x^– intermediates formed during reactions with concentrated ClO₄^– promote irreversible Re complex decomposition and catalyst deactivation. The original catalyst design mimics the microbial ClO₄^– reductase, which integrates Mo(MGD)₂ complex (MGD = molybdopterin guanine dinucleotide) for oxygen atom transfer (OAT). Perchlorate-reducing microorganisms employ a separate enzyme, chlorite dismutase, to prevent accumulation of the destructive ClO₂^– intermediate. The structural intricacy of MGD ligand and the two-enzyme mechanism for microbial ClO₄^– reduction inspired us to improve catalyst stability by rationally tuning Re ligand structure and adding a ClO_x^– scavenger. Two new Re complexes, Re(O)(htz)₂Cl and Re(O)(hoz)(htz)Cl (htz = thiazolinyl-phenolato bidentate ligand), significantly mitigate Re complex decomposition by slightly lowering the OAT activity when immobilized in Pd/C. Further stability enhancement is then obtained by switching the nanoparticles from Pd to Rh, which exhibits high reactivity with ClO_x^– intermediates and thus prevents their deactivating reaction with the Re complex. Compared to Re(hoz)₂–Pd/C, the new Re(hoz)(htz)–Rh/C catalyst exhibits similar ClO₄^– reduction activity but superior stability, evidenced by a decrease of Re leaching from 37% to 0.25% and stability of surface Re speciation following the treatment of a concentrated “challenge” solution containing 1000 ppm of ClO₄^–. This work demonstrates the pivotal roles of coordination chemistry control and tuning of individual catalyst components for achieving both high activity and stability in environmental catalyst applications.