Beta Zeolite Si/Al Ratio
The SiO2/Al2O3 ratio (SAR) of Beta zeolite is the primary parameter controlling its acidity, hydrophobicity, and hydrothermal stability. Beta zeolite is commercially available with SAR values from approximately 10 to over 200.
Effect on Acidity
| Si/Al Range | Acidity Level | Best Applications |
|---|---|---|
| 10-25 | Very high | Maximum acid-catalyzed activity for hydrocracking, alkylation |
| 25-50 | High | General acid catalysis, SCR, isomerization |
| 50-100 | Moderate | Balanced acidity and stability, controlled coke formation |
| 100-200+ | Low (mild) | Hydrophobic adsorption, VOC removal, minimal coking |
Each framework aluminium atom generates one Brønsted acid site when in the proton-exchanged form. Lower Si/Al = more acid sites = higher catalytic activity, but also more rapid coke formation and higher sensitivity to hydrothermal deactivation.
Effect on Hydrophobicity
As the Si/Al ratio increases, the zeolite framework becomes increasingly hydrophobic. At SAR > 80, Beta zeolite preferentially adsorbs non-polar organic molecules over water vapour, making it suitable for VOC removal from humid exhaust streams and for reactions in aqueous environments.
Effect on Stability
Higher SAR Beta zeolites (> 50) demonstrate improved hydrothermal stability, retaining crystallinity under steam regeneration and high-temperature operating conditions. For applications requiring frequent oxidative regenerations (e.g., SCR, FCC additives), higher SAR grades are recommended despite their lower acid site density.
How to Choose
Select the SAR based on your primary objective:
- Maximum activity: SAR 20-50 (more acid sites, faster rates)
- Maximum stability: SAR 50-200+ (longer catalyst life, better regeneration tolerance)
- Hydrophobic adsorption: SAR 80-200+ (preferential organic adsorption over water)
For specific application-matched recommendations, see the Beta Zeolite applications page. Request a sample with your target SAR.
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