Light alcohols as well as hydrocarbons can be obtained from the selective conversion of syngas over supported molybdenum catalysts. It is shown in this study that the activity and the selectivity are very much dependent on the support, the molybdenum content and the alkaline promoter, Indeed the methanol selectivity improves when molybdenum is supported on zinc oxide and promoted with potassium, Moreover, we found that the rate of methanol formation is in good correlation with unreduced molybdenum species. A dual-site mechanism is proposed for the methanol synthesis on such catalysts involving hydrogen activation (and dissociative carbon monoxide adsorption for hydrocarbons formation) and non-dissociative carbon monoxide adsorption, respectively, on reduced and unreduced molybdenum species.