Zeolite SCR for NOx Removal

Zeolite-based SCR (Selective Catalytic Reduction) is the dominant technology for NOx removal from diesel exhaust and an increasingly preferred option for stationary sources. Zeolite catalysts convert NOx to nitrogen and water with ammonia (or urea-derived ammonia) at 150-600 °C, combining a wide active temperature window with the hydrothermal stability that vanadium-based catalysts cannot offer above ~550 °C.

How Zeolite SCR Removes NOx

Ammonia reacts selectively with NO and NO₂ over the zeolite’s metal-exchanged active sites:

• 4 NO + 4 NH₃ + O₂ → 4 N₂ + 6 H₂O
• NO + NO₂ + 2 NH₃ → 2 N₂ + 3 H₂O

The “selective” in SCR means ammonia is directed toward NOx reduction rather than oxidation by the excess oxygen always present in exhaust gas.

Zeolite Families for NOx Removal

Cu-SSZ-13 vs Fe-SSZ-13 for NOx

Cu-SSZ-13 is the benchmark for mobile diesel: >90% NOx conversion at 200 °C, with the CHA framework protecting copper against migration during 800 °C DPF regeneration. Fe-SSZ-13 is preferred when exhaust contains significant SO₂ (above 10-20 ppm) or when operation concentrates in the 350-550 °C window.

NOx Removal Applications

• On-road diesel (Euro VI / EPA / China 6): Cu-SSZ-13, DOC + DPF + SCR aftertreatment
• Non-road mobile (construction, agriculture): Cu-SSZ-13, high durability
• Marine: Fe-SSZ-13 for residual-fuel sulfur levels
• Stationary (boilers, gas turbines, process heaters): Cu-SSZ-13, Fe-SSZ-13, or Cu/Fe-Beta

For the full catalyst selection comparison, see best zeolite for SCR and Cu-SSZ-13 vs Fe-SSZ-13. When requesting a sample, specify your application, exhaust temperature range, fuel sulfur content, and emission standard.