We have used density functional theory (DFT) to investigate the adsorption and first dissociation step of ammonia on both clean and Pt-covered TiO2 rutile (1 1 0) surfaces. On clean rutile TiO2 (1 1 0) surface, NH3 and NH2 prefer to chemisorb on the five-coordinated titanium (Ti5c) site, and H is adsorbed favorably on the bridging oxygen (01) site, while a single Pt atom prefers to adsorb on the hollow (H2) site. It is found that the preadsorbed Pt atom enhances significantly the adsorption of NH3, NH2 and H species on rutile TiO2 (1 1 0) surface by binding with Pt adatom directly. It is also found that the first dissociation step of ammonia (NH3 >= NH2 + H) on the clean rutile TiO2 (1 1 0) surface is endothermic by 0.89 eV, and no transition state exists. In addition, the first dissociation step of ammonia on Pt-covered rutile TiO2 (1 1 0) surface is found to be endothermic by only 0.43 eV, but presents an activation energy barrier of 1.82 eV. A comparison of the adsorption and first dissociation step of ammonia on rutile TiO2 (1 10) surface with and without Pt adatom has been discussed. Investigations indicate that the adsorbed Pt adatom on clean rutile TiO2 (1 1 0) surface not only changes the surface electron structure, but also varies the reaction pathways by participating in the reaction. It is expected that our results would provide useful information for the development of catalyst for NH3 dissociation. (C) 2011 Elsevier B.V. All rights reserved.