Density functional theory model for calculating pore size distributions: pore structure of nanoporous catalysts

Abstract

Using the example of nanoporous catalysts, we discuss the non-local density functional theory (NLDFT) model applied to physical adsorption of nitrogen and argon. The model has been used for predicting adsorption/desorption isotherms in nanopores of different geometries over a wide range of pore sizes (0.5–100 nm), and for calculating pore size distributions from adsorption isotherms based on given intermolecular fluid–fluid and fluid–solid potentials. The development of new nanoporous catalysts requires reliable characterization methods. We critically analyze different methods which are currently used for pore structure characterization in the range of nanometers. Calculations of the pore size distributions from nitrogen and argon adsorption isotherms are presented. Our primary method is based on the NLDFT model of adsorption on MCM-41, developed earlier. The results obtained with the NLDFT model are compared with other methods. It is shown, that the pore structure of nanoprous catalysts can be quite complex, and that Ar and N2 isotherms contain complimentary information. The NLDFT model is recommended for evaluation of pore size distributions in nanoporous catalysts and other MCM-41 based materials.