Rh Nanoparticles\nEncaged in Hollow Porous Silica Nanospheres\nas Catalysts for Toluene Hydrogenation under Mild Reaction Conditions

In this work, we report Rh nanoparticles encaged in hollow\nporous\nsilica nanospheres (Rh@HPSNs) as highly active toluene hydrogenation\ncatalysts under mild reaction conditions. Poly(ethylenimine)/poly(acrylic\nacid) (PEI/PAA) micelles in a water–ethanol system were used\nas templates for silica deposition to synthesize core–shell-structured\nsilica-coated PEI/PAA micelles, which were further soaked in a solution\nof Rh precursors, washed, calcined, and subsequently reduced by H<sub>2</sub> to obtain Rh@HPSNs, featuring small Rh nanoparticles in highly\nporous hollow silica nanospheres. The synthesized Rh@HPSNs illustrate\nhigh catalytic activities for toluene hydrogenation at 0.1 MPa H<sub>2</sub> and 30 °C and achieve a methylcyclohexane yield of >99%\nat a reaction time of 2.0 h and a toluene/Rh ratio of 500/1. To our\nbest knowledge, Rh@HPSNs are comparable to state-of-the-art Rh-based\ncatalysts at mild conditions for toluene hydrogenation, and the enhancement\nis ascribed to small-sized Rh particles efficiently utilizing the\nRh metal, highly porous hollow silica nanospheres to accelerate mass\ntransfer, and the protections of silica shells to the inner catalytic\nfunctionalities.