Chromium oxide nano-particles with an average diameter of 3 nm covered by amorphous carbon (CrO x /C) were successfully synthesized. The synthesized CrO x /C materials were used for the selective catalytic reduction of NO x by NH 3 (NH 3 -SCR), which shows superb NH 3 -SCR activity and in particular, satisfactory regeneration ability in the presence of SO 2 compared with Mn-based catalysts. The as-prepared catalysts were characterized by XRD, HRTEM, Raman, FTIR, BET, TPD, TPR, XPS and in situ FTIR techniques. The results indicated presence of certain amounts of unstable lattice oxygen exposed on the surface of CrO x nano-particles with an average size of 3 nm in the CrO x /C samples, which led to NO being conveniently oxidized to NO 2 . The formed NO 2 participated in NH 3 -SCR activity, reacting with catalysts via a "fast NH 3 -SCR" pathway, which enhanced th NH 3 -SCR performance of the CrO x /C catalysts. Furthermore, the stable lattice of the CrO x species made the catalyst immune to the sulfation process, which was inferred to be the cause of its superior regeneration ability in the presence of SO 2 . This study provides a simple way to synthesize stable CrO x nano-particles with active oxygen, and sheds light on designing NH 3 -SCR catalysts with highly efficient low temperature activity, SO 2 tolerance, and regeneration ability.