Previous research shows that lattice oxygen of Cu catalyst participates in the methanol conversion. In this study, Cu/ZnO catalyst was pretreated to become fully oxidized, partially reduced, or completely reduced. In situ diffuse-reflectance infrared Fourier-transformed spectroscopy (DRIFTS) was used to analyze the methanol (MeOH) adsorption at 393 K and a following stepwise temperature-programmed desorption (sTPD). In addition to methoxy and formates appeared after MeOH adsorption, Cu/ZnO catalyst had formaldehyde but no CO2 while the Cu was completely reduced. When the Cu was in the oxidized or partially reduced states, CO2 formed and more formate appeared. Lattice oxygen participated in the MeOH conversion, and the reactivity was higher in the partially reduced Cu/ZnO than in the oxidized Cu/ZnO. This suggests that reduced Cu catalyzes the reaction between MeOH adspecies and lattice oxygen. (C) 2011 Elsevier B.V. All rights reserved.