Hyperpolarised xenon MRI and time-resolved X-ray computed tomography studies of structure-transport relationships in hierarchical porous media

Catalysed diesel particulate filter (DPF) monoliths are hierarchical porous solids, as demonstrated by mercury porosimetry. Establishing structure-transport relationships, including assessing the general accessibility of catalyst, is challenging, and, thus, a comprehensive approach necessary. Contributions, from each porosity level, to transport have been established using hyperpolarised (hp) xenon-129 magnetic resonance imaging (MRI) gas dispersion within DPF at variable water saturation, since X-ray Computerised-Tomography, and 1H 2H NMR methods, shown that levels dry out progressively. At high hp 129Xe MRI showed between channels monolith predominantly taking place channel wall intersections with macroporosity. The walls themselves make relatively small contribution through due distribution micro-/meso-porous washcoat layer away intersections. Only low when smallest pores opened, do MR images became strongly affected relaxation. This observation indicates paramagnetic (catalytic) centres for gases arises only once open.