Determination of the fractal dimension of alumina using adsorption: Challenges of choosing appropriate adsorbates and analysis methods

Authors

  • Elsa M. R. Capitaine,

    1. Department of Chemical & Petroleum Engineering, University of Calgary, Calgary, Alberta, Canada T2N 1N4
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  • Josephine M. Hill

    Corresponding author
    1. Department of Chemical & Petroleum Engineering, University of Calgary, Calgary, Alberta, Canada T2N 1N4
    • Department of Chemical & Petroleum Engineering, University of Calgary, Calgary, Alberta, Canada T2N 1N4.
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Abstract

The classical method for surface characterisation of the porous structure of the catalysts is nitrogen (N2) adsorption at −196°C, which provides a catalyst surface area value valid for molecules similar in size to N2 (0.162 nm2/molecule). To complement and obtain more information about the materials, catalyst surfaces can be characterised using fractal geometry. The fractal dimension of a sample can be determined by the adsorption uptake of molecules of different sizes on the surface of interest in order to obtain a characteristic parameter of the surface geometry known as the fractal dimension, D. In this work, the value of D for a γ-alumina catalyst support has been determined (D = 2.71 ± 0.15) using different adsorbates (argon, nitrogen, isopropanol, pyridine, and n-butane). The decision process for choosing these adsorbates and the challenges of this type of characterisation method are discussed in this article. © 2011 Canadian Society for Chemical Engineering

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