Polyphenylene sulfide as an efficient solid-phase ligand for improved selective alkyne hydrogenation

Abstract

Liquid phase catalytic selective hydrogenation of alkynes to alkenes is a widely used reaction in the industry. Pairing nanocatalysts with soluble ligands or developing advanced catalytic nanostructures are two general protocols to realize preferable hydrogenation performance. However, both protocols are not cost-effective, and it is still challenging to achieve high selectivity and high activity with conventional hydrogenation nanocatalysts. In this work, commercial available, low-cost, and reactant-inert polyphenylene sulfide (PPS) is used as a new solid-phase ligand for palladium nanocatalysts in selective alkyne hydrogenation. Hydrogenation experiments have been carried out on different terminal and internal alkyne substrates, to investigate the universal effects of PPS on hydrogenation. As a result, over-hydrogenation and/or isomerization could be effectively suppressed upon the addition of solid PPS powders. The beneficial effects can be easily tuned by varying the PPS dosage. Importantly, both solid supported nanocatalysts and PPS can be simply separated via sedimentation and washing for subsequent experiments. A recycling experiment with PPS/Pd@CaCO3 has demonstrated the good cyclability (ten times of usage without much changes in effectiveness) of the catalyst system. X-ray photoelectron spectroscopy results indicate that the weak binding of PPS as a solid-phase ligand to nanocatalysts may contribute to the improved selective hydrogenation performance.