Aminopolymer–Silica Composite-Supported Pd\nCatalysts for Selective Hydrogenation of Alkynes

Abstract

A single-component, recyclable heterogeneous\npalladium nanoparticle\ncatalyst is described for the selective hydrogenation of alkynes.\nThe palladium nanoparticles are generated through reduction of Pd­(II)\nspecies loaded into a mesoporous silica material functionalized with\nbranched poly­(ethyleneimine) polymers. An array of composite catalysts\nwith similar polymer composition, palladium loading, and nanoparticle\nsize (∼2 nm) are prepared to understand the importance of the\npolymer attachment method, the metal reduction method, the polymer\nmolecular weight, and the oxide porosity. Each catalyst shows excellent\nactivity in room temperature, liquid phase hydrogenation of diphenylacetylene\nto selectively produce <i>cis</i>-stilbene. Interestingly,\nit was found that the rate of over-hydrogenation could be significantly\nreduced by increasing the support porosity and using a high-molecular-weight\npolymer. These single-component catalysts are competitive with the\nbest palladium catalysts known for the selective liquid phase hydrogenation\nof alkynes and can be easily recovered and recycled with no leaching\nof palladium detected, retaining high activities and selectivities\nover multiple cycles with a simple regeneration procedure.