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[Display omitted] • Au loading/particle size affects performance of Au/ZnO catalysts for CO 2 reduction. • Selectivity for methanol formation increases with Au particle size. • Partial overgrowth of the Au NPs during reaction. • Formation of O-vacancies during reaction. • r Overgrowth/vacancy formation increases/decreases with Au loading and particle size. Methanol synthesis by CO 2 reduction is an important approach for energy storage. Aiming at a reduction of the catalyst mass in technical applications, we have investigated the influence of increasing Au loading on the performance of Au/ZnO in methanol and CO formation from CO 2 reduction. Using the same type of ZnO support, increased Au loading resulted also in a pronounced increase in Au particle size. The Au-mass-normalized reaction rate for methanol formation and TOF decrease with increasing Au loading/particle size, while the selectivity for methanol formation increases. CO adsorption monitored by in situ FTIR revealed a pronounced decrease of the accessible Au surface area during reaction, independent of the Au loading, pointing to a partial encapsulation of the Au nanoparticles by a partly reduced ZnO x , as described by SMSI effects. Possible reasons responsible for these effects and Au loading/size effects therein are discussed, strategies for future work are outlined. [ABSTRACT FROM AUTHOR]