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In order to understand the effects of the surface acid sites in mesoporous zeolites on the adsorption and diffusion of hydrocarbons, the adsorption and diffusion of n -heptane and toluene (two C 7 hydrocarbons) over the mesoporous HZSM-5 zeolites (SiO 2 /Al 2 O 3 = 36) were investigated. The adsorption isotherms of two C 7 hydrocarbons over the mesoporous HZSM-5 zeolites showed the experimental data good fitting to dual-site Langmuir-Freundlich model (DSLF) similar to mesoporous NaZSM-5. Henry's constants and the initial heats of adsorption displayed stronger interactions in HZSM-5 than in NaZSM-5, especially for n -heptane, due to the presence of surface acid sites. The influence of acidity to the adsorbate-adsorbent interactions decreases with increasing of the mesoporosity. The investigation on the diffusion of n -heptane and toluene in mesoporous HZSM-5 samples by the zero-length column (ZLC) method showed the strong interaction of adsorbates and HZSM-5 samples by effective diffusivity and activation energy. Moreover, the diffusions of adsorbates in zeolites were advanced with the introduction of mesopores in the zeolitic samples, though the dramatic influence of mesopore to diffusion is not arisen in mesoporous NaZSM-5, reflecting larger influence of acid sites on diffusion in mesoporous HZSM-5 samples. [ABSTRACT FROM AUTHOR]

Adsorption and diffusion properties of n-octane in meso-structured HZSM-5 zeolites were studied by high precision intelligent gravimetric analysis (IGA) and ZLC technology between 293 K and 393 K. As expected, great increase in adsorption capacity and diffusion efficient of n-octane in the mesostructured HZSM-5 zeolites was observed compared with conventional HZSM-5. At the same time, the adsorption activation energy of n-octane in the mesostructured HZSM-5 zeolites was significantly decreased. The adsorption heats with low n-octane loading showed a clear decline with increase of mesoporosity in the zeolite samples. These results clearly indicate that introduction of mesopores into the zeolites offered a short diffusion path and high diffusion rate for reactants and products, which resulted in a high yield of fuel oil and an enhanced resistance against the catalyst deactivation in the reaction of methanol to gasoline. [ABSTRACT FROM AUTHOR]

Abstract: A series of zeolite composites with hierarchically porous structures and tunable acidities were prepared. The structural, crystalline, and textural properties of the as-synthesized materials, as well as the reference Y and β zeolite samples, were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM)/transmission electron microscopy (TEM) analyses, Fourier transform infrared spectroscopy (FTIR), and nitrogen adsorption/desorption techniques. The acidic properties of the surface were determined by in situ FTIR of adsorbed pyridine. The hierarchy factor is an appropriate tool to classify hierarchically structured materials, and the hierarchical pores of the as-synthesized zeolite composite samples were investigated during the catalytic cracking of isopropylbenzene. The results show that the catalytic activity of isopropylbenzene cracking over the catalysts has a linear dependence with their hierarchy factor (HF). The tunable acidities were tested by methanol dehydration to dimethyl ether (DME), and the dehydration activity of methanol over the catalysts shows a linear decrease with the increased Lewis/Brönsted ratio, while the selectivity of DME shows a linear increase with the enhanced Lewis/Brönsted ratio. [Copyright &y& Elsevier]