A　series　of　nitrogen　and　sulfur　(N/S)　co-doped　graphene　supported　catalysts　(Mn-Ce-SnOx/NSG)　were　synthesized　using　an　in　situ　method　for　enhancing　selective　catalytic　reduction　of　NOx　with　NH3　(NH3-SCR)　performance.　The　changes　in　catalysts’　structure,　morphology,　and　active　sites　were　systematically　researched　to　explore　the　promoting　effect　of　N/S　co-doped　on　catalytic　performance.　The　prepared　Mn-Ce-SnOx/NSG-0.3　catalyst　achieves　an　excellent　SCR　activity　at　a　low　temperature,　which　is　comparable　to　previous　graphene-based　catalysts.　The　Ce3+/(Ce3+　+　Ce4+),　Mn4+/Mn3+,　and　Oα/(Oα　+　Oβ)　ratios　in　the　catalyst　are　improved　by　N/S　co-doping,　which　closely　related　to　excellent　SCR　activity.　Meanwhile,　the　unpaired　electrons　on　N/S　functional　groups　are　effective　in　promoting　the　adsorption　and　further　oxidation　of　gaseous　NO.　The　ability　to　adsorb　NH3　has　also　been　promoted　result　of　numerous　Lewis　acid　sites　over　Mn-Ce-SnOx/NSG-0.3.　In-situ　DRIFTS　and　reaction　kinetic　results　suggest　that　the　Eley–Rideal　mechanism　should　be　the　most　significant　pathway　in　the　temperature　range　of　≥　200　°C,　where　coordinated　NH3　has　higher　activity　than　ionic　NH4+.　The　Langmuir-Hinshelwood　(L-H)　mechanism　is　the　main　route　of　the　low-temperature　(L-T)　(　©　2021