The　xCN/Ce-OMS-2　(x　is　the　nominal　weight　percentages　of　g-C3N4,　x　=　5.0,　10.0,　and　15.0　wt%)　catalysts　were　prepared　via　an　in-situ　synthesis　method.　Physicochemical　properties　of　the　as-prepared　materials　were　measured　by　means　of　the　XRD,　TEM,　SEM,　BET,　XPS,　H2-TPR,　NH3-TPD,　and　in-situ　DRIFTS　techniques,　and　their　catalytic　activities　for　the　selective　catalytic　reduction　of　NOx　with　NH3　(NH3-SCR)　at　low　temperatures　were　evaluated.　Among　all　the　catalysts,　the　10CN/Ce-OMS-2　catalyst　showed　the　widest　temperature　span　for　NH3-SCR　reaction　and　the　best　resistance　to　SO2　poisoning.　This　may　result　from　that　the　modification　of　g-C3N4　promoted　the　electron　transfer　in　catalyst,　not　only　increased　the　concentration　of　active　Mn4+　species　and　chemisorbed　oxygen　species,　but　also　improved　the　surface　acidity　of　the　catalyst.　In-situ　DRIFTS　results　further　showed　that　the　modification　of　g-C3N4　increased　the　amount　of　acid　sites　and　enhanced　the　formation　of　NH3　or　NO　intermediates　(i.e.,　monodentate　and　bidentate　nitrate),　which　enhanced　the　reaction　activity　of　the　catalyst.