Adsorption and Diffusion Properties of Toluene on Y Zeolites by Steam-Acid Treatment: Effects of Mesoporosity and Surface Acidity

Owing to the great importance of zeolite Y in industrial catalysis, the adsorption equilibrium and diffusion of toluene on a series of steaming and acid leaching Y zeolites were investigated to obtain an insight into the effects of secondary mesoporosity and surface acidity in the Y zeolites on the adsorption and diffusion properties. The adsorption isotherms of toluene on the treated Y zeolites can be fitted favorably by the dual-site Toth model relative to the single-site Toth model of the initial micropore Y zeolite. The temperature-dependent parameters including maximum adsorbed amount q(s), affinity constant b, isosteric heat of adsorption Q, Henry's constant K-H, and initial heat of adsorption Q(st) were discussed in terms of the microporosity, mesoporosity, and acidic site density, revealing the enhancement of the adsorbed amount and the weakening of the toluene-zeolite interaction of the Y zeolite after steam-acid treatment. The diffusion of toluene on the Y zeolite was examined by means of desorption curves from the zero-length column chromatography technique. The correlation of the effective diffusion time constant D-eff/R-2 and the activation energy E-a with meso-/microporosity and acidic site density reveals that the diffusion is improved with the decreasing strength of the interaction between toluene and zeolite and the increasing meso-/microporosity in the Y zeolite.