Adsorption and diffusion of toluene on Na and Cs mordenites for hydrocarbon traps

In this work, we report results of toluene adsorption on Cs-exchanged Na mordenite with different Cs loadings. Breakthrough curves were obtained, from which adsorption capacities at different gas phase concentration and temperatures could be calculated. Temperature-programmed desorption experiments were used in order to assess the strength of toluene–zeolite interactions. Pulse chromatographic experiments combined with moment analysis allowed us to obtain adsorption and diffusion constants.The results show that the addition of a small amount of Cs (2 wt%) produces an increase in both the toluene adsorption capacity and the interaction strength. A higher amount of Cs (up to 19 wt%) also results in an increase of the toluene–zeolite interaction strength, but the adsorption capacity decreases due to steric effects. Pulse chromatographic experiments show that the diffusion coefficient of toluene increases with the increase of the Cs loading, which is probably a consequence of the increase of the external surface of the mordenite crystals. For the different samples, diffusion coefficients vary in the 10−14–10−17 cm2 s−1 range with activation energies between 55 and 65 kJ mol−1.

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► The addition of a small amount of Cs improves the toluene adsorption capacity.
► A higher amount of Cs increases of the toluene–zeolite interaction strength.
► Basicity and steric effects modulate the adsorption for hydrocarbon traps.