Jean Rouquerol

Recommendations for the characterization of porous solids (Technical Report)

These recommendations aim to be a tool for the selection and appraisal of the methods of characterization of porous solids, and to also give the warnings and guidelines on which the experts generally agree. For this purpose, they successively consider the description of a porous solid (definitions, terminology), the principal methods available (stereology , radiation scattering, pycnometry, adsorption, intrusion, suction, maximum buble pressure, fluid flow, immersion or adsorption calorimetry, thermoporometry , size exclusion chromatography, Xenon NMR and ultrasonic methods) and finally the general principles which are worth being followed in the selection of the appropriate method.

Physisorption of gases, with special reference to the evaluation of surface area and pore size distribution (IUPAC Technical Report)

Abstract Gas adsorption is an important tool for the characterisation of porous solids and fine powders. Major advances in recent years have made it necessary to update the 1985 IUPAC manual on Reporting Physisorption Data for Gas/Solid Systems. The aims of the present document are to clarify and standardise the presentation, nomenclature and methodology associated with the application of physisorption for surface area assessment and pore size analysis and to draw attention to remaining problems in the interpretation of physisorption data.

Is the BET equation applicable to microporous adsorbents

This chapter focuses on how the BET equation is applicable to microporous adsorbents. The BET method can be considered, essentially, as a mathematical means to analyze the adsorption isotherm to derive a “monolayer capacity” and then a surface area. The BET method should not be applied to adsorbents containing micropores in every case. Beyond the “linearity criterion” of the BET plot, two other criteria are found necessary, especially in the presence of micropores, to draw the specific advantage of the BET equation. Calorimetric data for adsorption on microporous adsorbents confirm the fact that the BET monolayer content mostly corresponds to the adsorbate in energetical interaction with the surface. For adsorbents containing micropores, the concept of “BET monolayer content” is misleading and could well be replaced by that of “BET strong retention capacity.” This concept includes the adsorbate present in the micropores together with the content of the statistical monolayer on the non-microporous portion of the surface.

Controlled transformation rate thermal analysis: the hidden face of thermal analysis

Abstract Controlled transformation rate thermal analysis is defined here as a general thermoanalytical method where, instead of controlling the temperature (as in conventional thermal analysis), one controls some other physical or chemical property, which is made to follow a pre-determined programme by appropriate heating of the sample. The historical development of the method is reviewed (from the early sixties) together with its analytical, preparative and kinetic applications. Examples given mainly deal with adsorbents, catalysts and ceramics. The paper ends with a list of expected developments.

Calorimetric determination of surface areas: Possibilities of a modified Harkins and Jura procedure

Abstract The immersion calorimetric method of Harkins and Jura for determining specific surface areas of powders was reexamined in the light of results obtained with 11 powders of different chemical nature and having specific surface areas ranging from 0.6 to 129 m2 g−1. Microcalorimetric determinations were performed, using water (and, to a smaller extent, butanol, pentanol, and n-decane) as the adsorbate and as the immersion liquid. Less than two water layers appears to be enough to “screen” completely the solid surface. This leads to a modified procedure which avoids the previous shortcomings arising from interparticulate condensation and also from the thickness of the preadsorbed layer. The experimental reproducibility is of ±0.1 m2 g−1 ± 1% (of the measured value).

Two-dimensional freezing of nitrogen or argon on differently graphitized carbons

Abstract On a set of differently graphitized carbon blacks (Sterling heated between 1500 and 2700°C), chosen to reproduce, in some respects, the set used in 1954 by Beebe and Young (J. Phys. Chem. 58, 93) in their famous experiments, adsorption microcalorimetry at 77 K gives experimental evidence of a two-dimensional fluid → solid phase change at the completion of the argon or nitrogen monolayer. That phenomenon (which is confirmed by a slight substep of the isotherms) develops earlier (i.e., on a less graphitized surface) in the case of argon than in the case of nitrogen: This is explained by the epitaxial crystallization of nitrogen which makes it very sensitive to the size of the graphitic sheets.

Possibilities of two non-isothermal procedures (temperature- or rate-controlled) for kinetical studies

The applicability of both conventional Thermal Analysis (TA) and Controlled Rate Thermal Analysis (CRTA) for kinetic analysis is discussed. It is shown that TA method can give a reliable kinetic information and meaningful kinetic parameters especially for solid state transformation. On the other hand the CRTA method is more suitable for decomposition process where one or more gasses are evolved.A consistent and reliable method of kinetic analysis is proposed for both techniques. This method is illustrated to analyze the crystallization process of chalcogenide glass and the decomposition of dolomite.ZusammenfassungEs wird die Anwendbarkeit von herkömmlicher Thermoanalyse (TA) und geschwindigkeitsgesteuerter Thermoanalyse (CRTA) bei kinetischen Untersuchungen diskutiert. Die TA Technik kann eine zuverlässige kinetische Information und sinnvolle kinetische Parameter besonders bei Feststoffumsetzungen liefern. Die CRTA Technik ist andererseits mehr für Zersetzungsprozesse geeignet, bei denen ein oder mehrere Gase freigesetzt werden.Für beide Techniken wird eine einheitliche und geeignete Methode zu kinetischen Analyse vorgeschlagen. Als Beispiel wird diese Methode zur Analyse des Kristallisationsprozesses von Chalkogenidgläsern sowie der Zersetzung von Dolomit angewendet.

Liquid intrusion and alternative methods for the characterization of macroporous materials (IUPAC Technical Report)

This document deals with the characterization of porous materials having pore widths in the macropore range of 50 nm to 500 μm. In recent years, the development of advanced adsorbents and catalysts (e.g., monoliths having hierarchical pore networks) has brought about a renewed interest in macropore structures. Mercury intrusion–extrusion porosimetry is a well-established method, which is at present the most widely used for determining the macropore size distribution. However, because of the reservations raised by the use of mercury, it is now evident that the principles involved in the application of mercury porosimetry require reappraisal and that alternative methods are worth being listed and evaluated. The reliability of mercury porosimetry is discussed in the first part of the report along with the conditions required for its safe use. Other procedures for macropore size analysis, which are critically examined, include the intrusion of other non-wetting liquids and certain wetting liquids, capillary condensation, liquid permeation, imaging, and image analysis. The statistical reconstruction of porous materials and the use of macroporous reference materials (RMs) are also examined. Finally, the future of macropore analysis is discussed.

Calcination of the MCM-41 mesophase: mechanism of surfactant thermal degradation and evolution of the porosity

Sample controlled thermal analysis (SCTA) has been used to carefully and reproducibly eliminate the organic surfactant template from pure silica mesoporous MCM-41. The reproducibility allowed a number of intermediate species to be isolated permitting complementary measurements. To understand the mechanisms by which the surfactant is removed, evolved gas analysis as well as 1H and 13C MAS NMR were used. The liberation of the porosity and evolution of the surface hydrophobicity were followed by gas adsorption, XRD and immersion microcalorimetry.It would seem that two types of cetyltrimethylammonium surfactant exist in the confined state, of which the large majority decomposes at a lower temperature (up to 200 °C) within the silica organic host than in the pure state. A small quantity of organic fragments are still observed within the pore structure up to 500 °C. Gas adsorption shows a pore blocking effect occurs during the surfactant removal.

Guidelines for the Characterization of Porous Solids

Abstract The aim of this paper is to give an impression of the work of the recently disbanded IUPAC Sub-Committee on the Characterization of Porous Solids. It provides a brief description of the development, content and philosophy of the Recommendations of the Sub-Committee, to be published in Pure and Applied Chemistry. An outline is given of the terminology required to define a porous solid and of the proposed general guidelines for the selection of the most appropriate methods of characterization.