Noble metal (Pt, Rh, Pd) promoted Fe-ZSM-5 for selective catalytic oxidation of ammonia to N₂ at low temperatures

We have reported previously the excellent performance of Fe-exchanged ZSM-5 for selective catalytic oxidation (SCO) of ammonia to nitrogen at high temperatures (e.g., 400-500°C). The present work indicates that the reaction temperature can be decreased to 250-350°C when a small amount of noble metal (Pt, Rh or Pd) is added (by both doping and ion exchange) to the Fe-ZSM-5. The SCO activity follows the order: Pt/Fe-ZSM-5 > Rh/Fe-ZSM-5 > Pd/Fe-ZSM-5. The noble metal promoted Fe-ZSM-5 catalysts also show higher activity for NH₃ oxidation than Ce-exchanged Fe-ZSM-5 at low temperatures. On the Pt promoted Fe-ZSM-5, near 100% of NH₃ conversion is obtained at 250°C at a high space velocity (GHSV = 2.3 × 10⁵ h^-1) and nitrogen is the main product. The presence of H₂O and SO₂ decreases the SCO performance only slightly. This catalyst is a good candidate for solving the ammonia slip problem that plagues the selective catalytic reduction (SCR) of NO with ammonia in power plants.