The response of a zeolite pellet to gas exposure is not governed only by the zeolite framework itself. Once the powder is formed into a compact body, packing, interparticle contact, local void structure and gastreatment
history may also influence the measured impedance response [1,2]
This study examines this issue for binder-free Ag-coated ZSM-5 pellets prepared from different sieved feed fractions and followed through the same CO2/N2 conditioning sequence. Two ZSM-5 pellets were compared:
one prepared from a 250-300 μm sieved feed fraction and one from a 400-450 μm sieved feed fraction of the same parent material. These fractions were used as pellet-fabrication feed fractions and were not treated as crystallite-size classes. The impedance response was analysed using electrochemical impedance spectroscopy (EIS), together with Nyquist, Bode and distribution of relaxation times (DRT) representations [2,3]
The two pellets did not behave as equivalent formed bodies under the CO2/N2 sequence. The 250-300 μm pellet retained a comparatively compact response envelope, whereas the 400-450 μm pellet showed stronger history-dependent redistribution, especially in the selected shorter-timescale DRT region. In both cases, CO2 exposure and subsequent N2 recovery displaced the response from the early reference region, but the magnitude of this displacement was larger for the 400-450 μm pellet. The resulting apparent/effective transport-response descriptors (Dinter and Dintra) are therefore interpreted as protocol-bounded responses metrics, not as intrinsic diffusion coefficients. Within this interpretation, EIS and DRT provide a useful comparative route for examining how formed zeolite pellets respond to CO2 exposure when their feedfraction-
derived pellet structure is changed.

References
[1] E. S. Grape, J. G. Flores, et al. J. Am. Chem. Soc. 142 (39), 16795, 2020.
[2] E. S. Grape, A. J. Chacón-García, et al. Nat Water 1 (5), 433, 2023.
[3] A. Raj, R. Rego, et al. Chemical Engineering Journal 453, 139757, 2023.
[4] T.-B. Liu, J.-W. Deng, et al. Inorg. Chem. Front. 11 (10), 3056, 2024.