Characterization of hierarchical pore structures in ceramics using multiscale tomography

The total activity, selectivity and lifetime of a heterogeneous silica-alumina catalyst depends on the flow of molecules through complex three-dimensional (3-D) hierarchical pore structures that span length scales from tens of microns to nanometers. Unlike traditionally used mercury intrusion porosimetry (MIP), 3-D imaging techniques, such as tomography, allow for the direct quantification of the pore structures. However, in tomography the field of view decreases as resolution increases. In this contribution a multiscale tomography (MT) approach was developed by combining X-ray microtomography, dual beam focused ion beam tomography and electron tomography to probe hierarchical porous structures in two silica-alumina catalysts sintered/calcined at 580 and 800 °C, respectively. Both MIP and MT revealed that sintering at 800 °C vs. 580 °C closed ∼15-20% of the porosity. MIP showed both catalysts having pores spanning the 3 nm to 10 μm range with bimodal pore distributions centred at ∼1 μm and