One-Step Synthesis of Size-Tunable Rhodium Nanoparticles on Carbon Nanotubes: A Study of Particle Size Effect on Hydrogenation of Xylene

Size-tunable rhodium (Rh) nanoparticles can be deposited uniformly on surfaces of carboxylate functionalized multiwalled carbon nanotubes (MWNTs) by a simple one-step sonochemical method in an ethanol solution containing RhCl3 and a series of boron-containing reagents of different reducing power. This technique provides a simple and rapid way of making rhodium nanoparticles of different size, which allows us to perform careful studies of particle size effect on catalysis. The hydrogenation of neat o-, m-, and p-xylene catalyzed by the MWNT-supported metallic Rh nanoparticle catalysts reveals a negative particle size effect (antipathetic structure sensitivity). The stereoselectivity of this reaction measured by the ratio of cis-/trans-dimethylcyclohexane increases with decreasing size of Rh nanoparticles.