ZSM-5 Si/Al Ratio
ZSM-5 offers a wide Si/Al range. The current standard catalogue covers 20-1000, while a documented 1500+ specialty grade extends the high-silica end for selected adsorption requirements.
Si/Al Ratio Spectrum
| Si/Al Range | Classification | Acid Site Density | Best Applications |
|---|---|---|---|
| 20-50 | Low SAR | Very high | FCC additives, alkylation, MTG |
| 50-200 | Medium SAR | Moderate | MTO/MTP, catalytic cracking, isomerization |
| 200-1000 | High SAR | Low | General acid catalysis, hydrophobic adsorption |
| 1000 standard; 1500+ specialty | Ultra-high SAR | Minimal | Trace VOC removal and hydrophobic adsorption evaluation |
Effect on Acidity
Each framework aluminium atom generates one Brønsted acid site. At Si/Al = 25, ZSM-5 has approximately one acid site per 25 framework T-atoms — high acidity suitable for cracking reactions. At Si/Al = 1500, acid sites are sparse and catalytic activity is minimal, but the framework is strongly hydrophobic.
Effect on Hydrophobicity
As Si/Al increases beyond ~200, the zeolite surface becomes dominated by siloxane (Si-O-Si) groups with very few polar Al-OH sites. At Si/Al > 500, ZSM-5 preferentially adsorbs non-polar organic molecules over water vapour — the basis for its use in VOC emission control from humid exhaust streams.
Effect on Crystal Morphology
ZSM-5’s Si/Al ratio correlates with available crystal morphologies:
- Nano polycrystal (N-series): Si/Al 30-60 — small spherical crystals for fast diffusion, MTG and FCC additives
- Single crystal rod (C-series): Si/Al 150-1500+ — well-defined rod-like crystals for adsorption and separation
How to Choose
| If You Need… | Choose ZSM-5 With… |
|---|---|
| Maximum cracking activity | SAR 20-50 (ZSM-5-N30, ZSM-5-25) |
| Balanced MTO/MTP performance | SAR 50-200 (ZSM-5-50, ZSM-5-C150) |
| VOC adsorption in humid air | SAR 300-1000 standard; 1500+ specialty |
| Trace organic removal | Evaluate the documented 1500+ specialty grade |
For detailed grade specifications, see the ZSM-5 specifications page. Request a sample with your target Si/Al ratio.
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