Mechanism of Reductive Fluorination by PTFE-Decomposition Fluorocarbon Gases for WO 3 .

Reductive fluorination, which entails the substitution of O from oxide compounds with F from fluoropolymers, is considered a practical approach for preparing transition-metal oxyfluorides. However, the current understanding of the fundamental reaction paths remains limited due to the analytical complexities posed by high-temperature reactions in glassware. Therefore, to expand this knowledgebase, this study investigates the reaction mechanisms behind the reductive fluorination of WO using polytetrafluoroethylene (PTFE) in an Ni reactor. Here, we explore varied reaction conditions (temperature, duration, and F/W ratio) to suppress the formation of carbon byproducts, minimize the dissipation of fluorine-containing tungsten (VI) compounds, and achieve a high fluorine content. The gas-solid reaction paths are analyzed using infrared spectroscopy, which revealed tetrafluoroethylene (CF), hexafluoropropene (CF), and iso-octafluoroisobutene (-CF) to be the reactive components in the PTFE-decomposition gas during the reactions with WO at 500 °C. CO and CO are further identified as gaseous byproducts of the reaction evincing that the reaction is prompted by difluorocarbene (:CF) formed after the cleavage of C═C bonds in -CF, CF, and CF upon contact with the WO surface. The solid-solid reaction path is established through a reaction between WO and WOF where solid-state diffusion of O and F is discerned at 500 °C.