Small gold nanoparticles supported on ZnO have been identified as highly active and selective catalysts for the green synthesis of methanol from CO2 and H-2. Furthermore, they can serve also a model system for the mechanistic understanding of methanol synthesis on the industrial Cu/ZnO catalyst. The dynamic changes in the structure of Au/ZnO upon exposure to methanol synthesis gas mixtures were studied using a combination of TAP reactor and near edge X-ray absorption spectroscopy (XANES) measurements at the Zn L-III edge, both in CO2/H-2 and CO/H-2 gas mixtures. TAP measurements indicated that CO can create significant amounts of O-vacancy defects in ZnO at 240 degrees C, while CO2 can re-oxidize a pre-reduced catalyst or maintain this state in the presence of strongly reducing gases (CO and H-2). Furthermore, CO2 present as reactant or resulting from the reactive removal of surface lattice oxygen by interaction with CO can be deposited on the pre-reduced Au/ZnO surface as stable adsorbed carbon containing species, e.g., as surface carbonates, which decompose at T >= 250 degrees C. In situ XANES measurements at the Zn LIII edge revealed that ZnO is significantly reduced during reaction, both in CO2/H-2 and CO/H-2 gas mixtures, but with the extent of the reduction being more pronounced in CO/H-2 than in CO2/H-2. These results will be critically discussed in the light of previous findings on the role of ZnO reduction in the activity of methanol synthesis catalysts.