Adsorption characterization of mesoporous molecular sieves

Low-temperature nitrogen and argon adsorption is one of the most informative experimental techniques for structural characterization of mesoporous molecular sieves (MMS). Although adsorption methods are well documented in the literature, the problem of quantitative interpretation of adsorption isotherms in terms of pore size distributions is quite topical. Conventional methods, such as the BJH and HK methods, are not adequate in the nanometer range of pore sizes typical for MMS. We discuss foundations and applications of the non-local density functional theory (NLDFT) for characterization of MMS. NLDFT is a molecular level model capable of constructing the adsorption isotherms in pores of different geometry and predicting the capillary condensation transitions in mesopores based on the potentials of intermolecular interactions. On the example of novel MCM-41 catalysts, we show that the NLDFT model is a reliable method for calculating the pore size distributions from adsorption isotherms, and in combination with XRD, for assessing the pore wall thickness in MMS of uniform structure.