Abstract— The Na+ and Ag+ forms of ZSM-12 zeolite microporous were used as effective adsorbents for hydrocarbons trap. Diffusion of a single adsorbed component including ethylene as a light molecule or toluene a heavier one inside a narrow one-dimensional channel was studied. Experimental desorption profiles for these two gases desorbing from both Ag-ZSM-12 and Na-ZSM-12 were obtained at very high heating rates comparable with the one observed during the cold start of a combustion engine. Numerical simulation based on Fick’s law and a transient diffusion boundary value yielded a good fitting of these experimental results. For both ZSM-12 forms considered in this study, diffusion activation energies Eω and EΞ for toluene are much higher than those for ethylene. The values of these parameters are higher for the Ag+ exchanged zeolite than for Na-ZSM-12 and related to the presence of strong Lewis acid sites in the former material. In addition each activation energy for Na-ZSM-12 and Ag-ZSM-12 decreases at increasing heating rate. This was explained by thermal vibrations of the zeolite lattice which allow higher diffusivity at high temperature.
Keywords— single component, single file diffusion, temperature-programmed desorption, ZSM-12
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