Studies on pore systems in catalysts: V. The t method

Pore size determination in modified micro- and mesoporous materials. Pitfalls and limitations in gas adsorption data analysis

Surface area and pore texture of catalysts

MCM-41 siliceous molecular sieves were used to test the applicability of the Kelvin equation for nitrogen adsorption in cylindrical pores of the size from 2 to 65 nm It was shown that the Kelvin equation for the hemispherical meniscus, corrected for the statistical film thickness, is in quite good agreement with an experimental relation between the pore size and the capillary condensation pressure The agreement can be made quantitative in the pore size range from ca 2 to 65 nm, if a simple correction to the Kelvin equation is introduced The required statistical film thickness curve (t-curve) was calculated using nitrogen adsorption data for large pore MCM-41 samples and the obtained results were extrapolated using an adsorption isotherm for a macroporous silica gel Moreover, an accurate analytical representation of the t-curve was found Since both the corrected Kelvin equation for cylindrical pores and the t-curve have simple analytical forms, they can conveniently be used in a variety of methods 

Application of large pore MCM-41 molecular sieves to improve pore size analysis using nitrogen adsorption measurements

The available literature on the crystal structure of the metastable alumina polymorphs and their associated transitions is critically reviewed and summarized. All the metastable alumina structures have been identified as ordered or partially ordered cation arrays on the interstitial sites of an approximately close-packed oxygen sublattice (either face-centered cubic or hexagonal close packed). The analysis of the symmetry relations between reported alumina polymorphs having an approximately face-centered cubic packing of the oxygen anions allows for an exact interpretation of all the complex domain structures that have been observed experimentally. Possible mechanisms for the phase transitions between the different alumina polymorphs also are discussed.

Metastable alumina polymorphs : Crystal structures and transition sequences

Thet-curve of multimolecular N2-adsorption

Studies on pore systems in catalysts I. The adsorption of nitrogen; apparatus and calculation

Bayerite, fl-AI(OH)3, and boehmite, 7-A1OOH, both with crystallite sizes of some tenths of a micron, were used for this investigation. The transformation of bayerite to T-alumina and of boehmite to 7and a for 7-alumina the oxygen sublattice is fairly well ordered, whereas the tetrahedral A1 lattice is strongly disordered. The crystallographic texture of 7and 7-alumina could be related to their microporous texture and this in its turn to the length of the OH bonds in the hydroxides. The formation of the well ordered super spinel structure ~-A120 3 is suppressed by obstructing the diffusion of the A1 ions either by the surface of numerous pores (T-alumina from bayerite or 7-alumina from gelatinous boehmite) or by incorporating large ions such as Na ions (y-alumina from crystalline boehmite). In these cases the disordered spinel type aluminas are transformed at a high temperature to 0and a-Al~O 3 by complete recrystallization to small particles which still have some preferred orientation.

Study of phase transformations during calcination of aluminum hydroxides by selected area electron diffraction

Valuable information about the specific surface area, the size, and the shapes of pores, the setting in of reversible capillary condensation and of complete filling of pores may be obtained by plotting the experimental volumes of adsorbed nitrogen, Vo, aa a function of the statistical thickness, 1, of the adsorbed layer, as given in Paper I of this series. The Va-t plot, together with the experimental adsorption and desorption isotherm gives a very good picture of the whole pore system. 1. va-t PLOTS

B.C. Lippens

Papers

Studies on pore systems in catalysts: V. The t method

Thet-curve of multimolecular N2-adsorption

Studies on pore systems in catalysts I. The adsorption of nitrogen; apparatus and calculation

Study of phase transformations during calcination of aluminum hydroxides by selected area electron diffraction

Studies on Pore Systems in Catalysts