Among various Cu/ZnO/ZrO2 catalysts with the Cu/Zn ratio of 3/7, the one with 15 wt.% of ZrO2 obtains the best activity for methanol synthesis by hydrogenation of CO. The TPR, TPO and XPS analyses reveal that a new copper oxide phase is formed in the calcined Cu/ZnO/ZrO2 catalysts by the dissolution of zirconium ions in copper oxide. In addition, the Cu/ZnO/ZrO2 catalyst with 15 wt.% of ZrO2 turns out to contain the largest amount of the new copper oxide phase. When the Cu/ZnO/ZrO2 catalysts is reduced, the Cu2+ species present in the ZrO2 lattice is transformed to Cu+ species. This leads to the speculation that the addition of ZrO2 to Cu/ZnO catalysts gives rise to the formation of Cu+ species, which is related to the methanol synthesis activity of Cu/ZnO/ZrO2 catalyst in addition to Cu metal particles. Consequently, the ratio of Cu+/Cu-0 is an important factor for the specific activity of Cu/ZnO/ZrO2 catalyst for methanol synthesis. (C) 2000 Elsevier Science B.V. All rights reserved.