Micromeritics GEMINI VII, Operator'S Manual

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B DFT Models
Using the modified Tarazona prescription described by Olivier (see DFT Model References on
page B - 17 [items 3 and 4]), model isotherms were calculated for a wide range of adsorptive
energies to a relative pressure of 0.6. The model makes no provision for pore filling in the
micropore region. If the sample solid contains small mesopores, the isotherm data should be
truncated (using the
Select Data Points window) to a suitably low relative pressure to avoid trying
to fit this region; mesopore filling reports as a large area of low energy in the calculated distribution
of adsorptive potential.
The surface energy is reported in terms of the effective Lennard-Jones interaction parameter, i.e.,
for the adsorptive / adsorbent pair divided by Boltzmann constant. The units are therefore Kelvin.
N2 - Cylindrical Pores - Oxide Surface
AR - Cylindrical Pores - Oxide Surface
Geometry: Cylinder
Substrate: Oxide
Category: Porosity
Method: Nitrogen at 77K; Argon at 87K
Model isotherms were calculated using a combination of statistical mechanical calculations and
experimental observations for macroporous silicas and MCM-41 mesoporous silicas as well as
zeolites. The pore-filling pressures were determined as a function of the pore size from adsorption
isotherms on MCM-41 materials characterized by X-ray and other techniques. The variation of the
pore fluid density with pressure and pore size has been accounted for by density functional theory
calculations. The N2 model reports pore sizes ranging from 3.8 to 387 Å and the AR model from
3.8 to over 500 angstroms.
References: M. Jaroniec, M. Kruk, J.P. Olivier, and S. Koch, “A New Method for the
Accurate Pore Size Analysis of MCM-41 and Other Silica-Based Meso-
porous Materials,” Proceedings of COPS-V, Heidelberg, Germany (1999).
N2 – Cylindrical Pores – Pillared Clay Surface (Montmorillionite)
Geometry: Cylinder
Substrate: Crystalline Silicate
Category: Porosity
Method: Nitrogen at 77K
Model isotherms were calculated using a combination of statistical thermodynamic Non-Local
Density Functional Theory (NLDFT) calculations and experimental isotherms for reference
samples of montmorillionite. The construction method for the hybrid models was analogous to that
described in the first reference below (Jaroniec et al,1999). The additional references add
additional theoretical details as well as examples of the application of the model to pillared clay
catalysts. This model reports pore widths from 3.8 to 387 angstroms.
B - 8
Gemini VII Operator Manual
239-42828-01 (Rev H ) — May 2021