title: A New Bioinspired Perchlorate Reduction Catalyst with Significantly Enhanced Stability via Rational Tuning of Rhenium Coordination Chemistry and Heterogeneous Reaction Pathway.
abstract: 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 ClOx(-) 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 ClOx(-) 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 ClOx(-) 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.
authors.affiliation: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.|Department of Civil and Environmental Engineering, Colorado School of Mines , Golden, Colorado 80401, United States.
authors.forename: Jinyong
authors.initials: J
authors.lastname: Liu
authors.affiliation: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
authors.forename: Mengwei
authors.initials: M
authors.lastname: Han
authors.affiliation: Department of Chemistry and Biochemistry, The Ohio State University , Columbus, Ohio 43210, United States.
authors.forename: Dimao
authors.initials: D
authors.lastname: Wu
authors.affiliation: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
authors.forename: Xi
authors.initials: X
authors.lastname: Chen
authors.affiliation: Department of Civil and Environmental Engineering, Clarkson University , Potsdam, New York 13699, United States.
authors.forename: Jong Kwon
authors.initials: JK
authors.lastname: Choe
authors.affiliation: Department of Civil, Architectural, and Environmental Engineering, University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Werth
authors.affiliation: Department of Civil and Environmental Engineering, Colorado School of Mines , Golden, Colorado 80401, United States.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Strathmann
mesh_terms: D002384:Catalysis; D008024:Ligands; D010084:Oxidation-Reduction; D010472:Perchlorates / Q000737:chemistry*; D012211:Rhenium / Q000737:chemistry*
chemical_list: D008024:Ligands; D010472:Perchlorates; D012211:Rhenium