This study compares the (nitrogen oxides) NOx photocatalytic degradation performance of the commercial bare semiconductors, titanium dioxide (TiO2 P25) and zinc oxide (ZnO), with that of the homemade gold (Au)-decorated semiconductors, Au/TiO2 and Au/ZnO (1 wt% Au). A plasmonic absorption band was observed at 550 nm for Au/TiO2 and around 700 nm for Au/ZnO. Aqueous dispersions based on these oxides were sprayed on mortar surfaces. The results revealed that Au/ZnO had a high NO degradation capability, comparable to that of TiO2 P25, and the best selectivity towards the formation of nitrates instead of NO2. The Au decoration clearly improved the photocatalytic response of ZnO, notably by avoiding the production of NO2. This positive effect was attributed to the better charge carrier separation and higher OH• production induced by the presence of Au. To the best of our knowledge, this was the first study on Au/ZnO used for NO photocatalytic degradation.