An ionic-liquid-like copolymer was used to stabilize the platinum nanoclusters in ionic liquids. Catalytic performance was tested by the selective hydrogenation of o-chloronitrobenzene. Platinum catalysts Pt-I (5.1 nm) and Pt-II (1.7 nm) both exhibited excellent activity and selectivity for the reaction and were recycled with the activity and selectivity preserved. An unprecedented total turnover number (>25,900) was obtained on the Pt-II catalyst. Infrared spectroscopy, transmission electron microscopy, X-ray diffraction characterizations, and density functional theory calculations were used to study the catalysts. (c) 2007 Elsevier Inc. All rights reserved.