The temperature-programmed start-up of a methanol reformer for the production of hydrogen by partial oxidation of methanol, using air as oxidant, was studied over a Cu/ZnO/Al2O3 sample in its oxidised, reduced, and reduced + air-exposed states. The temperature at which the reaction starts was shifted to higher values when the degree of surface oxidation increased: oxidised sample much greater than reduced sample > reduced + air-exposed sample. Conversely, the same product selectivity is observed irrespective of the initial state of the samples. Methanol partial oxidation over the oxidised sample was accompanied by concomitant surface reduction. This reduction process leads to surface reconstruction with a higher methanol decomposition capacity than that corresponding to prereduced counterparts. These differences appear to be related to changes in the number, but not in the characteristics, of the active sites induced by the different reduction potentials of the reacting gases. For consecutive start-ups, the reaction-reduced catalyst behaves identically to the prereduced counterparts. These observations point to the central role of lattice oxygen during the restructuring of the catalyst surface under reaction conditions.