The challenging catalytic oxidation of secondary alcohols is studied in different settings, both in the gas and complex liquid phase, as well as in batch and the more industrially relevant flow conditions. The research highlights phase-specific effects and addresses important issues such as the physical and chemical stability of the catalysts.

Abstract

Selective partial oxidation of alcohols is a straightforward synthetic pathway to access aldehydes and ketones, important building blocks for the chemical industry. The catalytic oxidation of higher secondary alcohols is challenging, which entails the need for low temperatures to preserve the selectivity or, in practice, the use of a liquid phase. In this work, we explored the applicability of Co-based spinel oxides as alternatives to noble metal-based supported catalysts for the oxidation of alcohols such as 2-butanol and 2-propanol. We developed a small-scale tri-phasic process in flow operable for consecutive weeks and using technical grade porous catalysts, en route to more industrially-relevant systems, focusing on the practical aspects of the process. Co₃O₄, MnCo₂O₄, NiCo₂O₄, ZnCo₂O₄, and CoFe₂O₄ were synthesized by combustion and characterized by XRD, SEM, EDX, XPS, N₂-physisorption, and FT-IR spectroscopy. The same catalysts were tested in batch in the liquid phase to explore the impact of the reaction conditions on the reaction outcome and to rule out flow-specific effects. Gas phase reactions unveiled the different behavior of the same catalysts in different environments, highlighting phase-specific effects such as the beneficial (liquid phase) versus inhibiting (gas phase) impact of Mn doping.