Pd Nanoparticles Supported on N-Incorporated Hybrid Organosilica as an Active and Selective Low-Temperature Phenol Hydrogenation Catalyst

A heterogeneous Pd-NPMO hybrid-silica catalyst is synthesized and its application for aqueous phase selective hydrogenation of phenol to cyclohexanone at near ambient temperature (40 °C) and under atmospheric hydrogen pressure is demonstrated. The homogeneously distributed Pd nanoparticles on N-bridged hybrid mesoporous organosilica showed remarkable activity and selectivity for cyclohexanone compared to the unmodified Pd-SBA-15 catalyst. Control experiments strongly claim the role of nitrogen domains in the organic framework of hybrid silica support in stabilizing small Pd nanoparticles and possibly modifying the Pd sites responsible for catalysis to activate the substrate molecules in water. The hybrid silica catalyst was stable and reused several times without any significant drop-in activity, proving the heterogeneity of the bifunctional Pd catalyst. Based on the density functional theory study and experimental interventions, a possible reaction mechanism for the low-temperature phenol hydrogenation explaining the role of organic domains in the hybrid-silica framework is proposed.