Cerium　oxide　(CeO2)　was　added　to　modified　Ru/TiO2　catalyst　by　a　two-step　impregnation　method　for　selective　catalytic　oxidation　of　ammonia　(NH3-SCO).　The　low-temperature　NH3　oxidation　activity　and　N2　selectivity　of　the　1Ru/xCe-TiO2　catalyst　were　investigated　with　the　result　that　both　SCO　activity　and　N2　selectivity　were　influenced　by　the　amount　of　Ce.　Specifically,　the　presence　of　5　wt%　CeO2　demonstrated　a　great　promoting　effect　on　both　parameters,　reaching　an　NH3　conversion　and　N2　selectivity　of　97　%　and　93　%　at　180　degrees　C,　respectively.　Various　characterization　methods　indicated　that　the　presence　of　CeO2　regulates　the　dispersion　of　the　1Ru/xCeTiO2　catalysts,　changes　the　amount,　strength　and　ratio　of　strong　and　weak　acid　sites　on　the　catalyst　surface,　and　promotes　the　formation　of　Ru-O-Ce　bonds　through　the　interaction　between　Ce　and　Ru　species,　which　facilitates　electron　transfer　and　oxygen　vacancy　formation,　thereby　enhancing　the　oxidation　ability　of　the　catalysts.　Furthermore,　the　results　of　in　situ　diffuse　reflectance　infrared　Fourier　transform　spectroscopy　indicated　that　the　NH3-SCO　reaction　over　the　1Ru/xCe-TiO2　catalysts　follows　the　＂internal＂　selective　catalytic　reduction　(i-SCR)　mechanism,　involving　the　oxidation　of　NH3　into　nitric　oxide　(NO)　species　and　the　reaction　of　-NH2　with　in　situformed　NO　to　form　N2.