Isothermal molecular beam experiments on the methanol oxidation over the stepped Au(332) surface were conducted under well-defined ultra-high vacuum conditions. In the measurements, a continuous flux of methanol at excess in the gas phase and pulses of atomic oxygen were provided to the surface kept at 230 K. The formation of the partial oxidation product methyl formate under the applied conditions was evidenced by time-resolved mass spectrometry, and accumulation of formate species, which resulted in a deactivation of the surface for methyl formate formation, was followed by in situ Infrared Reflection Absorption Spectroscopy measurements. The results suggest a different reactivity of oxygen accumulated during the oxygen pulses and atomic oxygen for the competing reaction pathways in the oxidation of methanol to the desired partial and the unwanted overoxidation products.