Characterization of micro- and mesoporous solids by physisorption methods and pore-size analysis

Abstract

Physisorption methods as routine tools for the characterization of micro- and mesopores of new materials have been explored. Crystalline zeolite structures of Na-Y and Na-ZSM-5, amorphous microporous mixed oxides, mesoporous SiO 2 and MCM-41 materials have been investigated and tested by a variety of methods to differentiate between meso- and microporous structures. Problems encountered with micropore analysis by routine application of the t-plot and the Horvath–Kawazoe method (HK) are identified. It is shown that neither type I isotherms nor t-plots, α s-plots or HK-pore-size distributions are reliable evidence for microporosity. The pore sizes in micropore-size distributions derived from the adsorption isotherm are very sensitive to adsorbate gas and adsorption temperature. Only with argon as the adsorbate at the temperature of liquid argon, reliable pore sizes in the micropore range are obtained. This manuscript attempts to guide scientists in the selection of suitable methods for the routine characterization of porous solids with commercial equipment based on our experiences.