The　Ce-Cu-SAPO-18　catalysts　were　prepared　by　the　ion　exchange　method.　The　Ce-Cu-SAPO-18-2　catalyst　with　a　Ce　content　of　1.24　wt%　showed　the　excellent　NH3-SCR　activity.　Characterization　results　demonstrated　that　the　Ce-Cu-SAPO-18-2　catalyst　possessed　strong　redox　ability　and　high　reactive　nitrate　and　NH3　species,　which　were　responsible　for　the　remarkable　SCR　performance.　The　best-performing　Ce-Cu-SAPO-18-2　catalyst　displayed　a　broad　operation　temperature　window,　a　result　possibly　due　to　the　improvement　of　physicochemical　properties　and　acceleration　of　reaction　rate　in　the　Langmuir-Hinshelwood　(L-H)　and　Eley-Rideal　(E-R)　mechanisms.　The　higher　amounts　of　isolated　Cu2+　species　and　acid　sites　in　Ce-Cu-SAPO-18.2　promoted　the　adsorption　and　activation　of　NO,　and　facilitated　the　reaction　between　the　adsorbed　NOx　species　and　the　gas-phase　NH3　molecules　according　to　the　L-H　mechanism.　For　the　E-R　mechanism,　the　NH3　(L)　species　were　the　crucial　initial　intermediates　for　NH3　activation,　and　the　more　amount　of　Lewis　acid　sites　in　the　Ce-Cu-SAPO-18-2　sample　originated　from　its　coordinatively　unsaturated　cationic　sites　benefited　the　reaction　between　the　adsorbed　NH3　species　and　NO　molecules.　Based　on　the　results　of　in　situ　DRIFTS　characterization,　we　believe　that　the　L-H　mechanism　dominated　the　NH3-SCR　reaction　at　low　temperatures,　and　the　doping　of　Ce　in　the　catalyst　improved　the　L-H　and　E-R　reactions　at　low　temperatures.