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Mojica-Sepúlveda RD, Mendoza-Herrera LJ, Muñoz M, Tebaldi MC. Textural Characterization by Using an Alternative Langmuir Isotherm and a New Thickness Function. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:11972-11982. [PMID: 36125418 DOI: 10.1021/acs.langmuir.2c01721] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Samples with micropores can not be adequately described by using the Langmuir isotherm. The Langmuir expression is obtained by using the monolayer assumption, which is not valid in samples with micropores. Then, we propose to include in the isotherm a corrective parameter related to the sample porosity. We show that the modified isotherm enables us to describe the experimental values for different samples (aluminas, clays, silicas, zeolites, and zirconias) in low and full relative pressure ranges. Indeed, a new thickness function for the adsorbate layer in terms of the relative pressure is proposed. Then, a better description of the external surface areas, mesopores, and micropores of the samples can be obtained with the new thickness function. The VBS model with this new thickness shows a better pore distribution description.
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Affiliation(s)
- Ruth D Mojica-Sepúlveda
- Centro de Investigaciones Ópticas (CONICET La Plata-CIC-UNLP), 1897La Plata, Argentina
- Departamento de Ciencias Básicas, Facultad de Ingeniería, Universidad Nacional de La Plata, 1900La Plata, Argentina
| | - Luis J Mendoza-Herrera
- Centro de Investigaciones Ópticas (CONICET La Plata-CIC-UNLP), 1897La Plata, Argentina
- Departamento de Ciencias Básicas, Facultad de Ingeniería, Universidad Nacional de La Plata, 1900La Plata, Argentina
| | - Mercedes Muñoz
- Centro de Investigación y Desarrollo en Ciencias Aplicadas, Dr. J. J. Ronco, CINDECA-CCT CONICET La Plata-UNLP, Calle 47 No. 257, 1900, La Plata, Argentina
- Facultad de Ciencia Exactas, Universidad Nacional de La Plata, 1900 La Plata, Argentina
| | - Myrian C Tebaldi
- Centro de Investigaciones Ópticas (CONICET La Plata-CIC-UNLP), 1897La Plata, Argentina
- Departamento de Ciencias Básicas, Facultad de Ingeniería, Universidad Nacional de La Plata, 1900La Plata, Argentina
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Microporous Volumes from Nitrogen Adsorption at 77 K: When to Use a Different Standard Isotherm? Catalysts 2021. [DOI: 10.3390/catal11121544] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
This work reviews the application of various standard isotherms to evaluate the micropore volume in a range of microporous materials. The selected materials have quite different surface chemistry, and are relevant due to their properties for adsorption and catalysis: zeolites, activated carbons, clay-based materials and MOFs. Some cases were analysed before and after being used as supports in the heterogenization of homogeneous catalysts. The discussion is centred, but not limited, to the three standard isotherms that are mostly employed in the literature (t-curve, non-porous carbon and non-porous hydroxylated silica) for the assessment of the micropore volume. For a given material the values of the micropore volumes from the different standard isotherms were compared, particularly against the values from the largely used t-curve. The cases where major discrepancies were found could normally be ascribed to samples that have a broad micropore size distribution.
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Galarneau A, Mehlhorn D, Guenneau F, Coasne B, Villemot F, Minoux D, Aquino C, Dath JP. Specific Surface Area Determination for Microporous/Mesoporous Materials: The Case of Mesoporous FAU-Y Zeolites. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:14134-14142. [PMID: 30379547 DOI: 10.1021/acs.langmuir.8b02144] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
A methodology for determining the micropore, mesopore, and external surface areas of hierarchical microporous/mesoporous materials from N2 adsorption isotherms at 77 K is described. For FAU-Y zeolites, the microporous surface area calculated using the Rouquerol criterion and the Brunauer-Emmett-Teller (BET) equation is in accord with the geometrical surface determined by the chord length distribution method. Therefore, BET surface area ( SBET) is the well representative of micropore surface areas of microporous materials and of total surface area of microporous/mesoporous materials. Mechanical mixtures of mesoporous MCM-41 and microporous FAU-Y powders of known surface areas were used to calculate the respective surface areas by weighted linear combination and the results were compared to the values obtained by the t-plot method. The first slope of the t-plot determined the mesopore and external surface areas ( Smes+ext). The linear fit of the first slope is in general in the range 0.01 < p/ p0 < 0.17 and contains the volumes and relative pressures at which all micropores are filled ( p/ p0 > 0.10). Overestimation of Smes+ext values was evident and appropriate corrections were provided. External surface areas ( Sext) were obtained from the second slope of the t-plot, without noting an overestimation of Sext, thus allowing the determination of mesopore surface areas ( Smes) by difference. Micropore surface areas were calculated by subtracting Smes+ext from the total surface area, SBET. As an example, this methodology was applied to characterize a family of hierarchical microporous/mesoporous FAU-Y (FAUmes) synthesized from H-FAU-Y (H-Y, Si/Al = 15) using C18TAB as the surfactant and different NaOH/Si ratios (0.05 < NaOH/Si < 0.25). By increasing the NaOH/Si ratio in the synthesis of FAUmes, it was shown that as the micropore surface area decreases, the mesopore surface area increases, whereas the micropore and mesopore surface area remains constant. This methodology allows accurate characterization of the surface areas of microporous/mesoporous materials.
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Affiliation(s)
- Anne Galarneau
- ICGM UMR 5253 CNRS-Univ Montpellier-ENSCM , ENSCM, 240 Av Pr E. Jeanbrau , 34296 Montpellier Cedex 5 , France
| | - Dirk Mehlhorn
- ICGM UMR 5253 CNRS-Univ Montpellier-ENSCM , ENSCM, 240 Av Pr E. Jeanbrau , 34296 Montpellier Cedex 5 , France
| | - Flavien Guenneau
- Sorbonne Université, CNRS, Collège de France, Laboratoire de Chimie de la Matière Condensée, LCMCP , F-75005 Paris , France
| | - Benoit Coasne
- Laboratoire Interdisciplinaire de Physique (LIPhy) , CNRS and University Grenoble Alpes, Domaine Universitaire , 140 rue de la Physique , BP 87, 38402 Saint Martin d'Heres Cedex , France
| | | | | | - Cindy Aquino
- Total Research & Technology Feluy , 7181 Feluy , Belgium
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