Low Temperature Ammonia Synthesis from Atomic N and Water on Rutile TiO₂(110)^†

We have investigated the formation of ammonia (NH₃) from atomic N and water (H₂O) on a rutile(R)-TiO₂(110) surface using the temperature-programed desorption method. The formation of NH₃ can be detected after coadsorption of atomic N and H₂O on the R-TiO₂(110) surface, desorbing from the 5-fold coordinated Ti⁴⁺ (Ti_5c) sites at about 400 K, demonstrating that the NH₃ formation on R-TiO₂(110) is feasible at low surface temperature. During the process, both hydroxyl groups at the bridging oxygen rows and H₂O on the Ti_5c sites contribute to the formation of NH₃, which are affected by H₂O coverage. At low H₂O coverage, the direct hopping of hydrogen atoms may be the dominant process for hydrogen transfer; while H₂O-assisted hydrogen atoms diffusion may be preferred at high H₂O coverage. Our result will be of significant help to get a deeper insight into the fundamental understandings of hydrogenation processes during the NH₃ synthesis.