Magnetically Recyclable Core–Shell Structured Pd-Based Catalysts for Semihydrogenation of Phenylacetylene

Magnetic core–shell structured Pd-based catalysts (Fe3O4@M/Pd, M = SiO2, AlOOH, TiO2, Cu3(BTC)2, and ZIF-8) were prepared and applied to semihydrogenation of phenylacetylene. The catalysts were characterized by various techniques, and it was found that the predominant chemical state of Pd species on the catalyst surface was PdO2, which was stable under the reaction condition (40 °C and 0.1 MPa H2). Among all the catalysts studied, Fe3O4@ZIF-8/Pd showed the highest selectivity to styrene, which was also superior to conventional catalysts such as Pd/C, Pd/Al2O3 and Lindlar catalyst. The high selectivity of Fe3O4@ZIF-8/Pd was mainly ascribed to the electronic effect between PdO2 and ZIF-8. Further investigation revealed that the phenylacetylene hydrogenation on Fe3O4@ZIF-8/Pd was solvent-dependent with the activity increasing with the solvent polarity. Among eight solvents tested, methanol was the most effective, with high and stable selectivity to styrene (around 92%) at complete conversion of phenylacetylene (≥99.5%) during five consecutive cycles.