We investigated the reduction behavior of Cu2+ species supported on gamma-Al2O3 in vacuo at high temperature by combined use of electron paramagnetic resonance (EPR) detecting highly dispersed Cu2+ species and photoluminescence spectroscopy monitoring isolated Cu+ ions. In the case of low loaded alumina-supported copper catalysts (Cu2+/Al2O3), there are isolated Cu2+ species centered in tetragonal distorted octahedra. It was found that the isolated Cu2+ species are easily reduced to Cu+ ions by thermovacuum treatment for Al2O3-supported catalyst, which are different from the past report for copper exchanged zeolites. On the other hand, the less dispersed Cu2+ species cannot be fully reduced to Cu+ ions in vacuo at 973 K on the alumina surface. (C) 2004 Elsevier B.V. All rights reserved.