Photodecomposition of NH3 to H-2 and N-2 was carried out using metal-supported TiO2 (M/TiO2) photo catalysts in an aqueous NH3 solution under UV irradiation at room temperature. Ni/TiO2 photocatalysts indicated the highest yield of H-2. The NH2 radical was formed as a dominant intermediate during NH3 decomposition, as confirmed by electron spin resonance measurements. Reaction pathways via NH2 radical formation were also investigated in detail by density functional theory. The results showed that H-2 and the H2N-NH2 as intermediate were formed by the coupling of an NH2 radical and an NH3 molecule in the gas phase during the photodecomposition of NH3. We believe that our findings would be useful for further developing efficient catalytic systems. (C) 2017 Elsevier B.V. All rights reserved.