SSZ-13 Zeolite Catalyst for SCR and NOx Abatement

SSZ-13 is a high-silica CHA aluminosilicate zeolite that has become the global benchmark catalyst for selective catalytic reduction (SCR) of NOx in diesel exhaust. Its 8-membered ring windows (~3.8 A) and chabazite cage structure provide an ideal scaffold for copper ion exchange, producing highly dispersed Cu²⁺ active sites that deliver >90% NOx conversion at temperatures as low as 200 °C.

Cu-SSZ-13 is the industry-leading formulation: it combines exceptional low-temperature SCR activity with hydrothermal stability that survives repeated exposure to 800 °C+ during diesel particulate filter (DPF) regeneration — a requirement that eliminated earlier-generation SCR catalysts. Fe-SSZ-13 offers an alternative for high-temperature and sulfur-containing exhaust streams where iron’s resistance to SO₂ poisoning outweighs copper’s superior low-temperature activity.

If your application is mobile diesel SCR (on-road, non-road, marine), Cu-SSZ-13 is the default choice. If your application is stationary NOx abatement with sulfur present in the fuel or exhaust, Fe-SSZ-13 or Beta zeolite may be more cost-effective.

How to Select the Right SSZ-13 Grade

SSZ-13 is not a single product — it is supplied in multiple forms depending on your manufacturing process and target application. Four parameters determine the right grade.

Si/Al ratio (SAR) controls the ion-exchange capacity and hydrothermal stability. Lower SAR (6-12) provides more framework Al sites for Cu or Fe exchange, maximizing active site density and low-temperature activity. Higher SAR (15-30) sacrifices some ion-exchange capacity but substantially improves hydrothermal durability — critical for applications where the catalyst sees repeated high-temperature excursions above 750 °C. For heavy-duty diesel SCR, SAR 12-18 balances both requirements.

Metal choice (Cu vs Fe) determines the operating temperature window. Copper-exchanged SSZ-13 delivers superior NOx conversion at 150-350 °C, the temperature range of light-duty and most heavy-duty diesel exhaust. Iron-exchanged SSZ-13 peaks at 350-550 °C and tolerates higher SO₂ concentrations, making it suitable for stationary engines, marine diesels burning high-sulfur fuel, and power plant SCR.

Metal loading typically ranges from 2-4 wt% for Cu and 1-3 wt% for Fe. Under-loading leaves active sites unused; over-loading leads to metal oxide clustering (CuO or Fe₂O₃) that reduces activity and can catalyze unwanted ammonia oxidation at high temperatures. The optimum is determined by the Si/Al ratio — higher Al content supports higher metal loading before clustering begins.

Precursor form depends on your manufacturing process. H-SSZ-13 (proton form) and NH₄-SSZ-13 (ammonium form) are the standard precursors for catalyst manufacturers who perform ion exchange in-house. Pre-exchanged Cu-SSZ-13 and Fe-SSZ-13 are supplied to coaters and system integrators who require ready-to-use catalyst powder with certified metal loading and dispersion.

Available SSZ-13 Grades

Custom SAR values (6-30) and metal loadings are available on request. Specify your target application, operating temperature range, and whether you require powder or washcoat-compatible form.

Key Specifications

All grades are supplied with batch Certificate of Analysis (COA) including SiO₂/Al₂O₃ ratio (XRF), BET surface area, metal loading (ICP-OES for exchanged forms), Na₂O content, particle size distribution, and XRD crystallinity.

SCR Performance: What Cu-SSZ-13 Delivers

Cu-SSZ-13 replaced Cu-ZSM-5 and Cu-Beta as the diesel SCR standard for a specific reason: hydrothermal stability. Earlier Cu-zeolite SCR catalysts lost significant activity after repeated exposure to temperatures above 650 °C during DPF regeneration. Cu-SSZ-13 retains >80% of its initial NOx conversion activity after hydrothermal aging at 800 °C for 16 hours — a standardized severe aging protocol that simulates full useful life.

Quantitative performance benchmarks for Cu-SSZ-13:

• NOx conversion at 200 °C: >90% (fresh), >80% (after 800 °C/16h hydrothermal aging)
• Operating window: 150-550 °C with >80% conversion
• N₂ selectivity: >95% across the operating window (minimizes N₂O greenhouse gas byproduct)
• Ammonia storage capacity: 0.8-1.2 mmol NH₃/g at 200 °C (supports high transient conversion)
• Hydrothermal stability limit: Retains CHA crystallinity to 850 °C (dry), 750 °C (10% steam)

Fe-SSZ-13 sacrifices some low-temperature activity for sulfur tolerance. In exhaust streams with 50-200 ppm SO₂, Fe-SSZ-13 retains >85% of its initial activity after 500 hours of exposure, where Cu-SSZ-13 may decline by 15-30% depending on temperature and SO₂ concentration.

See SSZ-13 for SCR for detailed operating conditions by application.

MTO and Other Applications

SSZ-13 can catalyze methanol-to-olefins (MTO) — it shares the same CHA topology as SAPO-34, the dominant MTO catalyst. However, SSZ-13’s stronger acidity produces lower total light olefin selectivity (60-75% vs SAPO-34’s 80-90%) and higher C₄+ byproducts. It is occasionally used in research or niche MTO applications where the higher propylene-to-ethylene ratio of aluminosilicate CHA is desired, but it does not compete with SAPO-34 as a commercial MTO catalyst.

SSZ-13 membranes and adsorbents are used in gas separation, particularly CO₂/CH₄ separation, where the 8-MR windows provide kinetic selectivity favoring CO₂ over methane.

Technical Documentation

• SSZ-13 Technical Data Sheet — Batch-level SiO₂/Al₂O₃, BET, XRD, metal loading, and particle size data
• SSZ-13 for SCR — Application-specific grade selection and operating conditions
• Best Zeolite for SCR — Cu-SSZ-13 vs Fe-SSZ-13 vs Beta comparison
• SAPO-34 vs SSZ-13 — CHA framework comparison: chemistry determines application

When requesting a sample, specify your target application (mobile SCR, stationary SCR, or other), required Si/Al ratio, desired metal form (Cu, Fe, or precursor), and preferred particle size range. We will recommend suitable SSZ-13 grades and provide technical documentation for evaluation.