Redox mechanism for selective oxidation of ethanol over monolayer V2O5/TiO2 catalysts

Abstract

The selective oxidation of ethanol to acetaldehyde and acetic acid over a monolayer V 2 O 5 /TiO 2 catalyst has been studied in situ using Fourier transform infrared spectroscopy and near-ambient pressure X-ray photoelectron spectroscopy (XPS) at temperatures ranging from 100 to 300 °C. The data were complemented with temperature-programmed reaction spectroscopy and kinetic measurements. It was found that at atmospheric pressure at low temperatures acetaldehyde is the major product formed with the selectivity of almost 100%. At higher temperatures, the reaction shifts toward acetic acid and at 200 °C its selectivity reaches 60%. Above 250 °C, the unselective oxidation to CO and CO 2 becomes dominant reaction. Infrared spectroscopy indicated that during the reaction at 100 °C, non-dissociatively adsorbed molecules of ethanol, ethoxide species, and adsorbed acetaldehyde are on the catalyst surface, while at higher temperatures the surface is mainly covered by acetate species. According to the XPS data, titanium cations remain in the Ti 4+ state, whereas V 5+ cations undergo a reversible reduction under reaction conditions. The presented data agree with the assumption that the selective oxidation of ethanol over vanadium oxide catalysts occurs at the redox V n+ sites via the redox mechanism involving the surface lattice oxygen species. A reaction scheme for the oxidation of ethanol over monolayer V 2 O 5 /TiO 2 catalysts is suggested.

Understanding the oxidative dehydrogenation of ethyl lactate to ethyl pyruvate over vanadia/titania

“…This is because of the formation of adsorbed acetate species. 60 Evidently, we detected the ethyl acetate by monitoring the mass signals during the temperature-programmed ethyl lactate desorption (Fig. S6).…”

Supported Vanadium Oxide Clusters in Partial Oxidation Processes: Catalytic Consequences of Size and Electronic Structure

“…Among these, Andrushkevich and collaborators have recently reported that titania‐supported monolayer vanadia displays a very high activity for ethanol partial oxidation (compared with similar systems at lower vanadium loadings). However, in this case a relative low selectivity to acetaldehyde was also reported and mainly acetic acid was observed as the main reaction product at 200 °C . Owing to a lack of control of the exact vanadia cluster size, the changes in the reactivity of VO x clusters with different morphologies is still subject of controversy and the exact determination of the active site is a topic of intense research .…”

MoO3–TiO2 synergy in oxidative dehydrogenation of lactic acid to pyruvic acid

“…[44][45][46] It has also been demonstrated that oxidative dehydrogenation of ethanol could be used as a model reaction to investigate the redox properties of V 2 O 5 /TiO 2 catalysts. 47 Inspired by these studies, we also applied ethanol oxidation as a model reaction to investigate these properties of the catalysts used for LA conversion. The catalytic results are summarized in Fig.…”