Hydrothermal Decomposition of Perfluoroalkyl Sulfonic Acids with Ruthenium on Carbon Catalyst

The application of heterogeneous catalysts for destruction of per- and polyfluoroalkyl substances (PFAS) in subcritical hydrothermal water (350°C, 16.5 MPa) is a promising remediation strategy. Among catalysts screened, carbon-supported noble metals (Ru/C, Rh/C, Pt/C, and Pd/C) were more effective than metal oxides (Al 2 O 3 , FeOOH, TiO 2 , and ZrO 2 ) at promoting degradation and defluorination of perfluorobutane sulfonic acid (PFBS), a representative perfluoroalkyl sulfonic acid (PFSA). After 3 h, PFBS and perfluorooctane sulfonic acid (PFOS) were degraded >98% and defluorinated >10% by a 5 wt% ruthenium-on-carbon (Ru/C) catalyst. Defluorination increased to >20% when reaction was extended to 5 h, but a large fraction of the fluorine mass balance remained unaccounted for. Mono-substituted PFSA intermediates were identified in solution and unextractable organic fluorine species on the Ru/C surface were confirmed by spectroscopic analysis. The bound species were released to solution as F - when exposing the Ru/C to hydrothermal alkaline treatment (HALT) conditions (1 M NaOH, 350°C), closing the fluorine mass balance. A tentative mechanism initiated by homolytic cleavage of carbon-carbon and carbon-sulfur bonds along the perfluoroalkyl chain is proposed, with chemisorbed fluorine resulting from coupling of C-centered radicals to the carbon support. These findings introduce an innovative strategy for more sustainable remediation of PFAS contamination. • Ru/C and other supported noble metals catalyze hydrothermal PFAS decomposition • Identified products include F - , short chain PFAS, and bound organofluorine species • Catalyst acts by promoting C-C bond cleavages along perfluoroalkyl chain • Use of catalyst eliminates the need for concentrated alkali amendments