Cu/MnO catalysts prepared via reduction of Cu-Mn spinel oxide were investigated for development of active Cu catalysts for the water gas shift reaction (WGSR). A Cu-Mn catalyst active for the WGSR was obtained after high temperature calcination at 900degreesC and subsequent reduction. The optimum Cu/Mn ratio for catalytic activity of the Cu-Mn oxide system was 1/2. Nonstoichiometric Cu1.5Mn1.5O4 phase existed stably when copper manganese oxide was calcined above 700degreesC. The optimized Cu-Mn spinel showed excellent WGSR activity when a larger percentage of CO was used, as in hydrocarbon reforming. Cu-Mn spinel oxides calcined above 900degreesC were easily reduced. This may be responsible for the high activity of the Cu/MnO catalyst. Carbon dioxide in the reformed gas significantly depressed WGSR activity below 200degreesC, while CO conversion reached equilibrium at 200degreesC in the absence of CO2. (C) 2003 Elsevier Science (USA). All rights reserved.