The production of ammonia from dinitrogen and water vapor at mild conditions of temperature and pressure on Fe{sup 3+}-doped titanium dioxide powders under UV radiation has been studied in a continuous photoreactor working in the gas-solid regime. A net activity decline was observed after a few hours of irradiation; this decline did not depend on the reactor temperature, the powder composition, or the amounts of produced ammonia. The highest activity is found when no excess iron is segregated at the surface; overall turnover numbers for dinitrogen reduction as high as six electrons per iron atom can then be reached before powder deactivation, showing the catalytic character of the participation of Fe in this process. An IR investigation of the active and spent specimens revealed that the irradiation determines the almost complete disappearance of the OH groups from the powder surface. Furthermore, an ESR study of all the powders showed that bulk Fe{sup 3+} ions are better electron traps than Ti{sup 4+} ions so that, when a UV photon generates a hole-electron pair, the electron can be stabilized on the iron ions.