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

Abstract

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.