Abstract: Through the study of the critical solution temperature of ionic liquids [CH₃(OCH₂CH₂)_nN⁺Et₃][CH₃SO₃^–] (IL_PEG, n = 12, 16, 22), IL_PEG-stabilized Rh nanoparticle catalysts have been found to function as thermoregulated phase-separable catalysts and have been shown to be efficient and recyclable for the selective hydrogenation of 1,5-cyclooctadiene (1,5-COD) to cyclooctene (COE). Under optimized conditions, the conversion of 1,5-COD and selectivity for COE were 99% and 90%, respectively. The Rh catalyst could be recovered by simple phase separation and reused for ten times without loss of activity or selectivity.

Key words: thermoregulated phase-separable catalysis, ionic liquid, rhodium nanoparticle, selective hydrogenation, 1,5-cyclooctadiene