Spatial distribution of coke residues in porous catalyst pellets analyzed by field-cycling relaxometry and parameter imaging

Not only relaxation times but also the diffusion coefficient is affected by the presence of coke residues in the pores. For macroscopically heterogeneous samples, they offer the possibility to generate maps of the local coke concentration by introducing appropriate filters into NMR imaging sequences. High-temperature regeneration of coked catalysts leads to such heterogeneous distributions which is visualized by T1 parameter imaging.