Application Guide
How gas adsorption is used to characterize CO₂ sorbents — zeolites, activated carbons, MOFs, and amine-functionalized supports — and why BET area alone does not predict capture performance.
Solid sorbents for CO₂ capture include zeolites (e.g. 13X), activated and polymer-derived carbons, metal–organic frameworks (MOFs), and porous silicas or polymers loaded with amines. Their uptake depends on two things: how much pore volume is available in the right size range, and how strongly the surface binds CO₂.
At the low CO₂ partial pressures of flue gas (around 0.1–0.15 bar) or air (around 0.0004 bar), uptake is dominated by narrow micropores and chemically active sites, not by total surface area. That is why two materials with the same BET area can differ several-fold in working capacity.
| Measurement | Probe / model | What it tells you |
|---|---|---|
| BET area | N2 at 77 K or Ar at 87 K, Rouquerol criteria | Apparent surface area for comparing batches and materials |
| Micropore size distribution | Ar at 87 K with NLDFT/QSDFT | Micropores without N2 quadrupole artefacts (IUPAC 2015 recommendation) |
| Ultramicropores (< ~0.7 nm) | CO2 at 273 K with a DFT/GCMC kernel | Narrow pores that N2 at 77 K fills too slowly to equilibrate |
| Mesopore volume of amine supports | N2 at 77 K, BJH/NLDFT before and after loading | How much pore volume the amine occupies and what remains for gas diffusion |
| CO2 isotherms at process temperature | Volumetric or gravimetric CO2 uptake | Capacity, isosteric heat (from two or more temperatures), selectivity estimates |
Use the calculators to convert test pressures to pore sizes, or email a short description of your sample and what you need to measure.