Over the past decades,the adsorption and decomposition of NH3 on metal oxide surfaces have attracted more and more attention.It is important in the separation and removal of not only ammonia but also nitrogen monoxide,nitrogen dioxide and dinitrogen oxide (NOx) from exhaust gas.The selective catalytic reduction (SCR) of NOx by NH3 is well-known selected to remove NOx where TiO2 based catalysts are the most used [1].In this study,the molecular and dissociative adsorption behaviors of NH3 on two common surfaces,(100) and (001) TiO2-B [2],which maintains the monoclinic structure as high as ~550℃ or higher in ambient conditions have been investigated using density functional theory (DFT) method.The investigation of surface reactivity towards NH3 shows that ammonia binds strongly to five-fold coordinated Ti carious on the surfaces.The obtained results confirm that the dissociative adsorption mode is much unfavorable than the molecular adsorption mode for NH-3 on stoichiometric TiO2-B surfaces.In addition,it proves that TiO2-B (100) surface shows considerable activity towards NH3 compared to TiO2-B (001) surface similar to the case of H2O [3].Three different coverages (1)1/6 ML; (2) 0.5ML (3)1ML are considered here to investigate the adsorption behavior of NH3 on TiO2-B surfaces.The adsorption energies decrease with the increase of NH3 coverage.