Role of Ion-Exchange Resins in Hydrogenation Reactions

The role of ion-exchange resins (IERs) as catalysts or catalysts supports, in hydrogenation reactions is revised and their potential application is presented. Both gel-type and macroreticular, basic or acid, IERs have been used for manifold metal-catalyzed hydrogenation processes in gas and liquid phase, including hydrogenation of alkenes, alkynes, carbonyls, arenes, nitroaromatics, and more. When available, qualitative relationships between the morphology and structure of resins and their performance as solid supports for metal catalysts are observed. Noble metals, such as Pt, Au, and Pd, and non-noble metals, such as Fe and Cu, have been introduced into IERs polymeric backbones by simple ion-exchange of a metal salt precursor with the resin, or by a combination of ion-exchange and other protocols, to obtain mono- and bimetallic catalysts supported on IERs. High yields towards target product, as well as the recyclability of metal-doped IERs, have been reported in the literature, with low metal leaching, which makes them highly interesting solid catalysts for a wide array of industrial applications. Multistep reaction processes, involving hydrogenation and hydration/cyclization/aldol condensation/etc., constitute promising applications due to the one-pot synthesis approach and relatively low temperatures required, which adds environmental interest in terms of process integration and optimization.