Microporous materials show increased reliability in surface area calculations at low pressure.
The BET equation was used to calculate the surface area of microporous materials like zeolites at different pressures. Results showed that surface area calculations are more reliable at relative pressures between 0.01-0.10. For most microporous materials, surface area calculated at 0.05-0.20 is lower than at 0.01-0.10. Some ZSM-5 samples show hysteresis loops at lower pressures, leading to smaller surface area calculations at 0.05-0.20 compared to 0.01-0.10. The more microporous material in catalysts, the larger the difference in surface area calculations between these pressure ranges. Pure zeolites can have up to a 15% difference in surface area calculations between these pressure ranges.