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Detection of the delayed condensation effect and determination of its impact on the accuracy of gas adsorption pore size distributions

Rigby, Sean P.; Husan, Muayad; Hitchcock, Iain; Fletcher, Robin S.

Authors

SEAN RIGBY sean.rigby@nottingham.ac.uk
Professor of Chemical Engineering

Muayad Husan

Iain Hitchcock

Robin S. Fletcher



Abstract

Macroscopic, highly disordered, mesoporous materials present a continuing challenge for accurate pore structure characterization. The typical macroscopic variation in local average pore space descriptors means that methods capable of delivering statistically representative characterizations are required. Gas adsorption is a representative but indirect method, normally requiring assumptions about the correct model for data analysis. In this work we present a novel method to both expand the range, and obtain greater accuracy, for the information obtained from the main boundary adsorption isotherms by using a combination of data obtained for two adsorptives, namely nitrogen and argon, both before and after mercury porosimetry. The method makes use of the fact that nitrogen and argon apparently ‘see’ a different pore geometry following mercury entrapment, with argon, relatively, ‘ignoring’ new metal surfaces produced by mercury porosimetry. The new method permits the study of network and pore–pore co-operative effects during adsorption that substantially affect the accuracy of the characteristic parameters, such as modal pore size, obtained for disordered materials. These effects have been explicitly quantified, for a typical sol-gel silica catalyst support material as a case study. The technique allowed the large discrepancies between modal pore sizes obtained from standard gas adsorption and mercury thermoporometry methods to be attributed to the network-based delayed condensation effect, rather than spinodal adsorption. Once the network-based delayed condensation effect had been accounted for, the simple cylindrical pore model and macroscopic thermodynamic Kelvin-Cohan equation were then found sufficient to accurately describe adsorption in the material studied, rather than needing a more complex microscopic theory. Hence, for disordered mesoporous solids, a proper account of inter-pore interactions is more important than that of intra-pore adsorbate density distribution, to obtain accurate pore size distributions.

Journal Article Type Article
Publication Date Mar 20, 2017
Journal Colloids and Surfaces A: Physicochemical and Engineering Aspects
Print ISSN 0927-7757
Electronic ISSN 0927-7757
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 517
APA6 Citation Rigby, S. P., Husan, M., Hitchcock, I., & Fletcher, R. S. (2017). Detection of the delayed condensation effect and determination of its impact on the accuracy of gas adsorption pore size distributions. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 517, https://doi.org/10.1016/j.colsurfa.2016.12.043
DOI https://doi.org/10.1016/j.colsurfa.2016.12.043
Keywords Adsorption; Pore-size distribution; Delayed condensation; Mercury porosimetry; FIB-SEM
Publisher URL http://www.sciencedirect.com/science/article/pii/S092777571631086X
Copyright Statement Copyright information regarding this work can be found at the following address: http://creativecommons.org/licenses/by-nc-nd/4.0

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Copyright Statement
Copyright information regarding this work can be found at the following address: http://creativecommons.org/licenses/by-nc-nd/4.0





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