Rhodium nanoparticles stabilized by the ionic-liq.-like copolymer N-Vinyl-2-pyrrolidone-1-vinyl-3-butylimidazolium chloride-1-vinyl-3-ethylimidazolium bromide copolymer were used to catalyze the hydrogenation of benzene and other arenes in ILs. The nanoparticle catalysts can endure forcing conditions (75 °C, 40 bar H2), resulting in high reaction rates and high conversions compared with other nanoparticles that operate in ILs. The hydrogenation of benzene attained record total turnovers of 20,000, and the products were easily sepd. without being contaminated by the catalysts. Other substrates, including alkyl-substituted arenes, phenol, 4-n-propylphenol, 4-methoxylphenol, and phenyl-methanol, were studied and in most cases were found to afford partially hydrogenated products in addn. to cyclohexanes. In-depth investigations on reaction optimization, including characterization of copolymers, TEM, and an IR spectroscopic study of nanocatalysts, were carried out.