One-Pot Liquid-Phase Synthesis of Methyl Isobutyl Ketone Over Bifunctional Ion-Exchange Resins: Unravelling the Role of Resins Structure and Active Pd or Cu Phases on Sintering, Leaching and Catalytic Activity

Abstract

This work evaluates the catalytic activity of gel-type and macroreticular sulfonic styrene-divinylbenzene ion-exchange resins (IERs) incorporating metallic Pd or Cu nanoparticles for the synthesis of methyl isobutyl ketone (MIBK) from acetone following a one-pot synthesis approach. The effects of reaction time, temperature, and metal loading on the catalytic activity are studied, along with reusability (batch) and stability (fixed-bed) tests, highlighting the industrial potential of the most active catalyst prepared consisting of Pd-embedded particles within a strongly acidic gel-type IER support. Pd-based catalysts are more active than Cu ones, reaching 100% selectivity to MIBK and yields to MIBK of 36%, similar to the commercial benchmark also tested for comparison, i.e. Amberlyst™CH28. The highest yield to MIBK (54%) is obtained at 120 °C, 30 bar of H₂, 300 rpm, a catalyst load of 5 wt% and a Pd loading of 1 wt% after 24 h, with margin to improvement since the catalytic activity is found to increase with temperature up to 130 °C without detectable by-products formation. The extensive characterization by several techniques (ICP-MS, SEM–EDS, N₂ physisorption, ISEC, TEM/HRTEM, and XRD) enabled to draw crucial conclusions to understand the role of IER morphology and metal used on the catalytic activity. Sintering of both Pd and Cu nanoparticles depends on the structural type of the resin support, being magnified for macroreticular resins due to an enhanced propensity towards particle coalescence in comparison to gel-type supports. The different extent of leaching observed for the Pd- or Cu- containing IERs is explained on a basis of the behavior of the corresponding metallic nanoparticles within the resins structure. The active metallic Pd or Cu phases have been identified by HRTEM, confirming the presence of metal oxide species.