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A single-component, recyclable heterogeneous palladium nanoparticle catalyst is described for the selective hydrogenation of alkynes. The palladium nanoparticles are generated through reduction of Pd(II) species loaded into a mesoporous silica material functionalized with branched poly(ethyleneimine) polymers. An array of composite catalysts with similar polymer composition, palladium loading, and nanoparticle size (∼2 nm) are prepared to understand the importance of the polymer attachment method, the metal reduction method, the polymer molecular weight, and the oxide porosity. Each catalyst shows excellent activity in room temperature, liquid phase hydrogenation of diphenylacetylene to selectively produce cis-stilbene. Interestingly, it was found that the rate of over-hydrogenation could be significantly reduced by increasing the support porosity and using a high-molecular-weight polymer. These single-component catalysts are competitive with the best palladium catalysts known for the selective liquid phase hydrogenation of alkynes and can be easily recovered and recycled with no leaching of palladium detected, retaining high activities and selectivities over multiple cycles with a simple regeneration procedure.
Long et al. (Fri,) studied this question.