Mechanistic Study of Electrocatalytic Perchlorate Reduction using an Oxorhenium Complex Supported on a Ti₄O₇ Support

Abstract

Developing a stable and active catalyst for ClO 4 − reduction at nonacidic pH has presented a significant challenge to the catalysis field. Previous research has demonstrated that by depositing an organometallic Re catalyst onto a Ti 4 O 7 support (Re/Ti 4 O 7 ), it was possible to stabilize the catalyst and obtain active electrocatalytic ClO 4 − reduction at circumneutral pH. Thus, the focus of this work was on elucidating the mechanisms of electrocatalytic ClO 4 − reduction in water with the Re/Ti 4 O 7 system. Density functional theory (DFT) simulations indicated that the adsorption of the Re catalyst was exothermic on Ti 4 O 7 , and X-ray photoelectron spectroscopy (XPS) characterization indicated that Re adsorption caused a net reduction of the Ti oxidation state on the Ti 4 O 7 surface. After ClO 4− reduction experiments, XPS results indicated the presence of Ti(0)/Ti(II) surface sites. Cyclic voltammetry experiments in an acetonitrile solvent provided supporting evidence that these surface sites were electroactive and likely participated in the ClO 4 − reduction reaction. Analysis of batch reduction experiments in acetonitrile via kinetic modeling estimated a catalyst turnover number of 332 ± 23, which provided further evidence that the reduced Ti sites could regenerate the Re catalyst. However, these reduced Ti sites were finite in number and required the production of adsorbed hydrogen via water reduction to facilitate continuous ClO 4 − reduction. DFT results indicated that the reduction of ClO 4 − to Cl − was exothermic and that reduced Ti sites participated in the reduction reaction. The experimental and DFT results allowed a preliminary mechanism for ClO 4 − reduction on Re/Ti 4 O 7 to be proposed.