Surface Chemistry of Perfluoro Ethers: An Infrared Study of the Thermal Decomposition of (C₂F₅)₂O on AI₂O₃

The adsorption and thermal decomposition of a model polyperfluorinated ether on high surface area AI₂O₃ has been studied using transmission infrared spectroscopy. It has been found that (C₂F₅)₂O interacts with the isolated OH groups on the AI₂O₃ surface, forming an increasing number of associated OH groups from 150 to 600 K. Surface fluoroacetate and surface fluoroformate species are also formed from the thermal decomposition of the (C₂F₅)₂O layer. At temperatures higher than 300 K, the surface fluoroacetate converts to surface fluoroformate. Oxidation of the (C₂F₅)₂O molecules also occuss on a surface preadsorbed with pyridine, indicating that Lewis acid Al³⁺ sites, blocked by pyridine adsorption, are not involved in fluoroacetate and fluoroformate production. The absence of a chemical reaction between the (C₂F₅)₂O adlayer and a (CH₃)₃SiCl-treated AI₂O₃ surface indicates that the presence of available surface hydroxyl groups is necessary for the oxidation of the perfluoro ether by AI₂O₃, A mechanism for the thermal decomposition of (C₂F₅)₂O on AI₂O₃ is proposed.