Selective Hydrogenations of Phenolic Compounds to Cyclohexanol Derivatives over Hollow Porous Silica Nanosphere-Confined Ru–ZnO _<i>x</i> Hybrid Nanoparticles

In this study, Ru–ZnOx hybrid nanoparticles (NPs) in hollow porous silica nanospheres (Ru–ZnOx@HPSNs) were reported for hydrogenations of phenolic compounds to cyclohexanol derivatives. The Ru–ZnOx@HPSNs were synthesized by the use of metal-ion-containing polymer micelle templates consisting of the chelate compounds of ethylenediamine with Ru/Zn ions, poly(ethylenimine), and poly(acrylic acid). With deposition of silica onto the templates, calcination to remove organics, and H2 reduction, Ru–ZnOx hybrid NPs encapsulated in hollow porous silica nanospheres were obtained. Ru–ZnOx@HPSNs exhibit ∼100% of cyclohexanol yield for phenol hydrogenation under 60 °C and 2.2 MPa of H2, and nearly 100% of cyclohexanol selectivity can be maintained even at low conversions. The mentioned catalysts are recyclable with good stability and show a wide substrate scope for hydrogenations of a series of phenolic compounds. Characterization suggests that the good selectivity and catalytic stability originate from Ru–ZnOx interaction, where the modulation of electronic/geometric properties induced by the Ru–ZnOx interaction accelerates the formation of cyclohexanol, and the confinement of catalytic functionalities inside hollow cavities improves their stability.