Using the chromatographic technique (carrier-gas: N2; tracer-gases: He, Ar) the effective diffusivity in single-pellet string columns (SPSC) packed with porous slab particles was studied. Dispersion due to extra-column effects was eliminated via convolution of column responses or two lengths. The measurements were done for cordierite particles and for cordierite coated with alumina-based washcoat. The effective diffusion coefficients for two tracer–carrier pairs were evaluated by fitting column response (chromatographic) peaks in time-domain. Mean transport parameters were evaluated for both types of porous particles. The obtained mean transport pore radii are in reasonable agreement with pore-size distribution from mercury porosimetry.