Synthesis of CrOx/C catalysts for low temperature NH3-SCR with enhanced regeneration ability in the presence of SO2

Abstract

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 NH₃ (NH₃-SCR), which shows superb NH₃-SCR activity and in particular, satisfactory regeneration ability in the presence of SO₂ 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 NO₂. The formed NO₂ participated in NH₃-SCR activity, reacting with catalysts via a “fast NH₃-SCR” pathway, which enhanced th NH₃-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 SO₂. This study provides a simple way to synthesize stable CrO_x nano-particles with active oxygen, and sheds light on designing NH₃-SCR catalysts with highly efficient low temperature activity, SO₂ tolerance, and regeneration ability.