Micelle-templated silicates as a test bed for methods of mesopore size evaluation

MCM-41-type micelle-templated silicates have been used as standard adsorbents to test usual methods of pore size evaluation in the diameter range 40-80 Angstrom. Pore sizes evaluated by XRD lattice parameters and void fraction have been used as standard values. Methods of pore size evaluation based on the Kelvin equation underevaluate the diameter of cylindrical pores by nearly 20%, unless the effect of the curvature radius of the adsorbent surface is taken into account. The Kelvin method modified according to Tolman or Broekhoff and de Boer accurately fits the experimental data. The 4V/S method also underestimates diameters by nearly 20% when a value a(N2) = 16.2 Angstrom(2) is used for the area covered by an adsorbed N(2) molecule in the BET surface area determination. The use of results from the cited literature, indicating a(N2) = 13.5 Angstrom(2) on the surface of hydroxylated silica, allows the 4V/S method to fit standard diameters. The empirical application to mesopores using the method of Horvath and Kawazoe is also discussed. (C) 1999 Elsevier Science B.V. All rights reserved.