Ethanol gas-phase ammoxidation to acetonitrile: the reactivity of supported vanadium oxide catalysts

Abstract

New insights on the gas-phase ammoxidation of ethanol to acetonitrile over supported vanadia catalysts were obtained by means of reactivity experiments (in ethanol ammoxidation and oxidation) as well as in situ Raman and DRIFT spectroscopy. It was found that the rate-determining step during the redox process depends on the support type. In the case of V₂O₅/ZrO₂, the V oxidation state under reaction conditions is closer to V⁵⁺, whereas with V₂O₅/TiO₂, the reduction of V⁵⁺ is faster than the re-oxidation of the corresponding reduced V species by O₂; thus, the V oxidation state under steady state conditions is lower than for V₂O₅/ZrO₂. In the latter catalyst, the more oxidized V species is responsible for ammonia activation and reaction with the intermediate acetaldehyde, leading in the end to a better acetonitrile yield than with V₂O₅/TiO₂. It was also found that V₂O₅/ZrO₂ is more selective to acetaldehyde than V₂O₅/TiO₂. With the former catalyst, ethanol is able to reduce V₂O₅ only to a limited extent. Conversely, V₂O₅/TiO₂ is readily reduced by ethanol but this reduced V species is responsible for an unselective oxidation of the alcohol, giving more CO and CO₂.