School of Chemistry

BET Analysis

BET Analysis: Anton Paar Quadrasorb Evo and Autosorb iQ-MP

Brunauer-Emmett-Teller (BET) analysis is used to evaluate the surface area of porous materials, such as catalyst supports or metal oxide frameworks. For accurate surface area measurements, the temperature and pressure of an inert gas are controlled to cause a single layer of gas molecules to be adsorbed over the entire surface of a solid. Pressure transducers respond quantitatively to the amount of gas adsorbed. Using these data, and the BET method, the specific surface area (surface area per unit mass, m²/g) of a sample can be calculated using the software.

As well as surface area, other physical properties of the analyte material can be determined using a variety of methods. This includes pore size distribution, total pore volume and average pore diameter.

Samples should be prepared as dry powders or small pellets, and in most cases 0.1 g of sample is sufficient. Clean, dry, 9 mm diameter glass cells should be used for BET analysis, and can be provided if necessary. Cells for the Evo and iQ are different in length (Evo cells approx. 28.5-29cm, iQ cells approx. X cm) so ensure you have the correct cells. The empty cell should be weighed before starting, and weighed again once the sample has been added to it, before the degassing step.

Training will take place over three consecutive days (approx 1 hour per day) so please plan accordingly. You should only request training once you have samples to run. The three days covers degassing, BET analysis, and data processing and cleanup. For the best results when degassing samples, please ensure you have an idea of what temperatures your material can withstand, as they should be degassed at the highest allowable temperature.

Please note that currently the only adsorbent gas the machines are equipped with is Nitrogen. The separate degassing unit (FloVac) used with the Evo machine and the in-built degasser on the iQ machine can be used at temperatures of up to 400 °C, but are most commonly used at between 150 and 300 °C.