Kinetics and Pathway of Vinyl Fluoride Reduction over Rhodium

Abstract

Fluorinated compounds have become prevalent in ecosystems because of their widespread use, yet few methods that can effectively degrade these pollutants exist. We investigated the catalytic reduction of vinyl fluoride (VF), a regulated high-volume chemical and probable carcinogen, over rhodium in H 2 gas or aqueous solution. Water controlled both the kinetics and products of VF reduction. In dry H 2 gas, VF was reduced through primarily hydrogenation, at rates that were too fast to measure. In liquid water, reaction was firstorder in both VF and rhodium concentrations and proceeded predominantly through hydrodefluorination. Experiments and calculations show the reaction was mass transfer-limited. Even adsorbed water molecules on the catalyst surface posed a significant mass transfer barrier and dramatically altered product selectivity. These results provide insights into the kinetics and pathway of VF defluorination and are important for the design of studies that aim to elucidate the reduction mechanisms of and develop treatment methods for fluorocarbons.

Reductive Defluorination of Branched Per- and Polyfluoroalkyl Substances with Cobalt Complex Catalysts

“…The bonding with the CC bond significantly weakens the tertiary C−F bond (364.4 kJ mol −1 , the lowest BDE among all structures). Similar results have been reported by Im et al, 47 who reported B 12 -catalyzed defluorination of the only sp 2 C−F bond in the refrigerant HFO-1234yf (H 2 CCF−CF 3 ) yielding H 2 CCH−CF 3 , and further defluorination of one sp 3 C−F bond in H 2 CCH−CF 3 yielding H 2 CCH−CF 2 H. Additionally, sp 2 C−F bonds can be cleaved with H 2 gas and a Rh/ Al 2 O 3 catalyst, 48,49 while sp 3 C−F bonds cannot. Defluorination involving unsaturated bonds probably follows reaction mechanisms similar to the Co-catalyzed dechlorination of chlorinated ethenes.…”

Catalytic reduction of water pollutants: knowledge gaps, lessons learned, and new opportunities

“…Due to the limit of our research experience and the length of this paper, we have not discussed PGM-catalyzed dehalogenation. Here we just briefly note that the switch from Pd (highly active in dechlorination) (Grittini et al, 1995;Lowry and Reinhard, 2000;Zhuang et al, 2011) to Rh enabled hydrodefluorination from fluoroarenes (Baumgartner and McNeill, 2012;Baumgartner et al, 2013;Yuan et al, 2021), vinyl fluoride (Yu and Chiu, 2014), and fluorinated pharmaceutical pollutants (Fig. 1) (Park et al, 2020).…”

Exploring beyond palladium: Catalytic reduction of aqueous oxyanion pollutants with alternative platinum group metals and new mechanistic implications

“…Computational studies [19,58] are also needed to provide detailed theoretical insights into these metal-specific effects and metal-substrate interactions. We emphasize that research priority should be given to further examining novel activity of these previously overlooked metals in water treatment applications, such as (1) exploring multi-functional activities in treating various emerging and challenging contaminants (e.g., nitro [59], fluoro [40][41][42][43] and polychloro [60,61]…”

“…However, our group recently found that a Rh/C catalyst exhibited substantially higher activity than Pd/C for ClO 3 − reduction in acidic solution [39]. In literature, Rh/Al 2 O 3 [40][41][42] and Pt/C [43] Samples were collected and filtered using the same procedures described above.…”