Characterisation of porous solids using a synergistic combination of nitrogen sorption, mercury porosimetry, electron microscopy and micro-focus X-ray imaging techniques

Abstract

Imaging methods, such as micro-focus X-ray (MFX) imaging and magnetic resonance imaging (MRI), have greatly improved our ability to characterise the highly complex internal structures of porous media. MFX imaging and MRI are now both able to provide maps of the spatial distribution of local average accessible porosity for mesoporous media over macroscopic length scales (>∼10 μm). A methodology for obtaining this type of information by MFX imaging is described here. For relatively chemically homogeneous materials, conventional ¹H MRI is also able to provide a map of the spatial distribution of local average pore size. However, there are limitations on the type of materials that may be studied using ¹H MRI and the range of information that may be obtained by utilising only one technique alone. For mesoporous materials, MFX imaging alone cannot currently map the spatial distribution of pore size. However, in this work it has been shown that the already extensive capabilities of MFX imaging may be even further enhanced by a combination of it with the more traditional techniques of mercury porosimetry and nitrogen sorption. The methodology described here has enabled the determination of the spatial distributions of both the local average (over length scales ∼10 μm) porosity and pore size distribution for mesoporous and macroporous materials over macroscopic length scales. The methodology is also suitable for quantitative application to interesting chemically heterogeneous materials, such as mixed oxide absorbents or coked catalysts, not amenable to conventional ¹H MRI.