Methanol (MeOH) conversion over a commercial Cu/ZnO/Al2O3 catalyst was investigated with different co-feed gas, namely, He, H-2, H2O or O-2 from 423 to 573 K. In-situ XRD results indicate that oxidic Cu was mostly reduced during the MeOH conversion reactions, except in the presence of O-2, when the Cu state seems to depend on the pretreatment. The steady-state activity follows: MeOH + O-2 > MeOH > MeOH + H-2 > MeOH + H2O. In the presence of H-2, a sequential H-abstraction of MeOH is indicated by the fact that formaldehyde (FAL) was produced at low MeOH conversion and CO dominated at high conversion. In the absence of H-2, no FAL was produced while CO dominated and some methyl formate (MF) was observed. Oxygen and water in the feed promoted CO2 formation and suppressed the formation of CO and ME A reaction scheme involving mainly H-abstraction and O-addition steps is proposed. (C) 2007 Elsevier B.V. All rights reserved.