Palladium Supported on an Acidic Resin: A Unique Bifunctional Catalyst for the Continuous Catalytic Hydrogenation of Organic Compounds in Supercritical Carbon Dioxide

Abstract 1% Palladium‐doped acidic resin (Amberlyst® 15; styrene‐divinylbenzene matrix with sulfonic acid groups) is shown to be a highly active catalyst for the continuous catalytic hydrogenation of CC bonds in supercritical carbon dioxide (scCO2) without affecting CO bonds. This 1% Pd/Amberlyst‐15 catalyst promotes the industrially important selective formation of 2‐ethylhexanal from crotonaldehyde in a “one‐pot” pathway involving hydrogenation and aldol condensation with a number of merits. The selectivity behavior of 1% Pd/Amberlyst‐15 is strikingly different compared to that of 1% Pd/C and 1% Pd/Al2O3 due to its prominent bifunctional nature based on sulfonic acid groups adjacent to metallic Pd sites. Hybrid “[Pdn–H]+” sites are suggested to act as both metal and acid sites promoting the bifunctional catalysis.