Ammonia　(NH3)　as　an　important　precursor　to　form　atmospheric　fine　particles　and　secondary　inorganic　aerosols,　should　be　strictly　controlled.　Photocatalysis　has　provided　a　facile　and　an　effective　way　to　eliminate　NH3　pollution　under　mild　conditions,　whereas　the　undesirable　products,　such　as　NO,　NO2　would　be　generated　during　the　reaction　and　the　mechanism　remains　unclear.　In　this　study,　F　or　Pt　modified　TiO2　were　explored　to　reduce　the　formation　of　NOx　during　photocatalytic　oxidation　of　low-concentration　NH3,　and　its　photocatalytic　activity,　selectivity　and　mechanism　of　NH3　conversion　were　systematically　studied.　Results　indicate　that　surface　fluorination　on　TiO2　contribute　to　the　reduction　of　noxious　NOx,　especially　for　NO2,　since　the　modified　TiO2　achieved　enhanced　adsorption　of　NH3　and　strong　electron-trapping　ability,　which　can　retard　the　recombination　of　photo　generated　electrons　and　holes.　In　addition,　the　deposition　of　Pt　could　further　extend　the　lifetime　of　the　electron　hole　pairs　by　strongly　capture　the　electron,　and　enhance　the　oxidation　of　NH3　into　nitrates　and　nitrites　species.　From　the　in-situ　DRIFT　spectroscopy　and　XPS　results,　we　can　deduce　that　reactive　amino　radical　(center　dot　NH2)　would　be　formed　on　TiO2　under　photoirradiation　after　the　adsorption　of　NH3　on　Lewis　acid　cites.　The　formed　center　dot　NH2　can　react　with　reactive　oxygen　species　in　the　presence　of　H2O,　and　produce　NOx　and　HNOx.　By　both　enhancing　the　adsorption　of　NH3　and　separation　efficiency　of　electron-hole　pairs,　the　presence　of　F　and　Pt　modification　on　the　TiO2　changes　the　photocatalytic　pathway　of　NH3　conversion.　The　proposed　selective　oxidation　mechanism　may　offer　a　novel　insight　into　the　photocatalytic　oxidation　of　atmospheric　NH3　on　other　metal　oxide　with　surface　modification　and　can　be　broadly　employed　in　air　pollution　control　in　indoor　environments.