Cu-SSZ-13 vs Fe-SSZ-13
Cu-SSZ-13 and Fe-SSZ-13 are the two commercial metal-exchanged forms of the CHA zeolite for SCR. Both share the same SSZ-13 framework, but the exchanged metal determines the temperature window, sulfur tolerance, and hydrothermal durability. The choice between them is driven by exhaust temperature profile, fuel sulfur content, and application.
Head-to-Head Comparison
| Property | Cu-SSZ-13 | Fe-SSZ-13 |
|---|---|---|
| Framework | CHA | CHA |
| Active metal | Cu²⁺ at 6-MR exchange sites | Fe³⁺/Fe²⁺ at exchange sites |
| NOx conversion at 200 °C | > 90% | Moderate (30-60%) |
| Peak activity window | 200-450 °C | 350-550 °C |
| SO₂ tolerance | Moderate | Superior (retains higher activity above 10-20 ppm SO₂) |
| Hydrothermal stability (800 °C/16h aging) | Retains > 80% conversion | Good, slightly lower low-T retention |
| N₂ selectivity | > 95% | High |
| Typical grades | SAR 12-18, Cu 2.0-3.0 wt% | SAR 15-30, Fe 1.5-2.5 wt% |
| Primary applications | Light/heavy-duty diesel | Marine, high-sulfur fuel, stationary |
When to Choose Cu-SSZ-13
Mobile diesel SCR — start with Cu-SSZ-13. No other zeolite matches its combination of low-temperature activity and hydrothermal durability. The CHA cage confines Cu²⁺ ions at six-membered ring positions, protecting them from the migration and agglomeration that deactivated earlier Cu-zeolites (Cu-ZSM-5, Cu-Beta) above 650 °C. SAR choice trades fresh activity against durability: SAR 12 for light-duty where peak activity matters most, SAR 18 for heavy-duty full-useful-life durability.
When to Choose Fe-SSZ-13
Sulfur-containing exhaust — evaluate Fe-SSZ-13. Copper-exchanged zeolites are sensitive to sulfur poisoning. At SO₂ concentrations above 10-20 ppm — typical of marine diesels burning residual fuel and stationary engines in regions without ultra-low-sulfur fuel — Fe-SSZ-13 maintains a higher fraction of its initial activity.
High-temperature operation — Fe-SSZ-13 has its peak where Cu declines. Above 450-500 °C, Fe-SSZ-13’s activity advantage over Cu-SSZ-13 grows, making it the better fit for high-temperature stationary applications.
Decision Guide
| Application | Recommendation |
|---|---|
| On-road diesel (Euro VI / EPA / China 6) | Cu-SSZ-13 |
| Heavy-duty diesel, maximum durability | Cu-SSZ-13, SAR 18 |
| Marine / high-sulfur fuel | Fe-SSZ-13 |
| Stationary, high temperature (350-550 °C) | Fe-SSZ-13 |
| Stationary, cost-sensitive, moderate temperature | Cu-SSZ-13 or Cu/Fe-Beta |
ZeoCatalyst supplies both forms — see the Cu-SSZ-13 product page and Fe-SSZ-13 product page. When requesting a sample, specify your exhaust temperature range, fuel sulfur content, and target emission standard.
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