Rh Nanoparticles Encaged in Hollow Porous Silica Nanospheres as Catalysts for Toluene Hydrogenation under Mild Reaction Conditions

In this work, we report Rh nanoparticles encaged in hollow porous silica nanospheres (Rh@HPSNs) as highly active toluene hydrogenation catalysts under mild reaction conditions. Poly(ethylenimine)/poly(acrylic acid) (PEI/PAA) micelles in a water–ethanol system were used as templates for silica deposition to synthesize core–shell-structured silica-coated PEI/PAA micelles, which were further soaked in a solution of Rh precursors, washed, calcined, and subsequently reduced by H2 to obtain Rh@HPSNs, featuring small Rh nanoparticles in highly porous hollow silica nanospheres. The synthesized Rh@HPSNs illustrate high catalytic activities for toluene hydrogenation at 0.1 MPa H2 and 30 °C and achieve a methylcyclohexane yield of >99% at a reaction time of 2.0 h and a toluene/Rh ratio of 500/1. To our best knowledge, Rh@HPSNs are comparable to state-of-the-art Rh-based catalysts at mild conditions for toluene hydrogenation, and the enhancement is ascribed to small-sized Rh particles efficiently utilizing the Rh metal, highly porous hollow silica nanospheres to accelerate mass transfer, and the protections of silica shells to the inner catalytic functionalities.