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

The classical method for surface characterisation of the porous structure of the catalysts is nitrogen (N 2 ) adsorption at −196°C, which provides a catalyst surface area value valid for molecules similar in size to N 2 (0.162 nm 2 /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