Determination of Mesopore Size Distributions from Argon Adsorption Data at 77 K

Abstract

Argon adsorption at 77 K on ordered mesoporous silicas (MCM-41, SBA-15) with pore diameters up to 9 nm and on disordered mesoporous silicas with larger pore sizes was investigated, allowing us to successfully develop a method to calculate pore size distributions (PSDs) for cylindrical pores with diameters below 15 nm. It was found that for argon at 77 K the capillary condensation pressure tends to gradually increase as the pore diameter increases up to about 15 nm, whereas larger mesopores do not exhibit capillary condensation. The capillary evaporation pressure was much less clearly related to the pore size, and the steepness of the desorption branch was not always correlated with the degree of structural ordering of a given adsorbent. A good correlation was found between the positions of capillary condensation steps on nitrogen and argon adsorption isotherms at 77 K, whereas the correlation between the positions of capillary evaporation steps was much worse. Therefore, for argon adsorption at 77 K, the ...