Thermal desorption of n-alcohols intercalated in vanadium pentaoxide hydrate

Abstract

The mechanism of irreversible adsorption and thermal desorption of n-alcohols, having carbon numbers m= 1–7, have been studied on V₂O₅·nH₂O by the use of thermal gravimetry, mass spectrometry, X-ray diffraction and Fourier-transform infrared spectroscopy. All the alcohols studied are dissociatively adsorbed as alkoxide by attacking the V–O bonds of the intralayer structure. Thermal desorption of alcohol occurs by one of, or a combination of, three processes: (1) molecular desorption, (2) evolution of chemical species produced by catalytic reaction with the substrate such as methanal (methanol), ethene (ethanol), propene (propan-1-ol)etc., (3) decomposition by combustion with oxygen of the layer structure to produce CO₂, CO and H₂O, which are desorbed, and decomposition products such as polymerized species and/or carbides, which are deposited in the solid. The formation of the latter compounds delays the structural changes of the solid to form oxides of vanadium ions of lower valency (e.g. V⁴⁺ and V³⁺).