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

Reductive fluorination, which entails the substitution of O 2- 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 3 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 (C 2 F 4 ), hexafluoropropene (C 3 F 6 ), and iso-octafluoroisobutene ( i -C 4 F 8 ) to be the reactive components in the PTFE-decomposition gas during the reactions with WO 3 at 500 °C. CO 2 and CO are further identified as gaseous byproducts of the reaction evincing that the reaction is prompted by difluorocarbene (:CF 2 ) formed after the cleavage of C═C bonds in i -C 4 F 8 , C 3 F 6 , and C 2 F 4 upon contact with the WO 3 surface. The solid-solid reaction path is established through a reaction between WO 3 and WO 3- x F x where solid-state diffusion of O 2- and F - is discerned at 500 °C.