Nitrate reduction on a Pt(100) electrode modified by Cu (Cu/Pt(100)) and Rh (Rh/Pt(100)) adatoms have been studied in alkaline media by means of cyclic voltammetry and in situ online electrochemical mass spectrometry (OLEMS). According to the cyclic voltammograms, nitrate reduction is catalyzed by both Cu/Pt(100) and Rh/Pt(100). Ammonia is the main product on the Rh/Pt(100) electrode in alkaline media. On Cu/Pt(100), the selective conversion from NO3- to N-2 may be achieved. The Cu sites catalyze the reduction of NO3- to NO2-, and the Pt(100) sites catalyze the reduction of NO2- to N-2, though in different potential windows.