Towards industrially-relevant liquid-phase flow oxidations of secondary alcohols over spinel cobaltites

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 for consecutive weeks and using technical grade microporous catalysts, en route to more industrially-relevant systems, focussing on the practical aspects of the process. Co3O4, MnCo2O4, NiCo2O4, ZnCo2O4, and CoFe2O4 were synthesised by combustion and characterised 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 behaviour of the same catalysts in different environments, highlighting phase-specific effects such as the beneficial (liquid phase) vs inhibiting (gas phase) impact of Mn doping.