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Aluminosilicate MCM-41 samples in the as-prepared form and modiÐed by deposition of carbonaceous compounds formed during conversion of cyclohexene were investigated by nitrogen adsorption. The amount of the deposits decreases with the reaction temperature and increases with the quantity of aluminium incorporated into the materials. The formation of coke occurs primarily in the aluminium-rich pores. The modiÐcation leads to a lowering of adsorption capacity, surface area, pore volume and relative pressure corresponding to the adsorption isotherm step that reÑects the capillary condensation. The nitrogen adsorption measurements appeared to be a useful tool for characterisation of structural and surface properties of both the original and the novel surface-modiÐed porous materials.

A study was carried out of ammonium ion sorption from synthetic aqueous solutions by Transcarpathian clinoptilolite, a natural zeolite, under static conditions. The main physical properties of the clinoptilolite and the basic parameters of its porous structure were determined. Values of the specific surface area and of the pore volume occupied by sorbed substances were calculated using the relative moisture content established and the maximum sorption capacity exhibited towards ammonium ions as well as a nitrogen adsorption/desorption method. Ammonium ion sorption by the zeolite appeared to be complete within 24 h for all fraction sizes, initial NH + 4 ion concentration and adsorbate volumes. The amounts of NH + 4 ions sorbed increased with increasing initial NH + 4 concentration and decreasing adsorbate volumes, with the maximum sorption capacity exhibited by the clinoptilolite being 0.64 mequiv/g. The sorption effectiveness decreased somewhat with increasing fraction size. The Langmuir and Freundlich models were applied to the data obtained from the batch studies with the first model exhibiting the more satisfactory correlation coefficient value (0.996 and 0.959, respectively).

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Sorption of benzene on nonsubstituted AlPO4-5 occurs on adsorption centers originating from surface heterogeneity and created by structure defects. The metallic heteroatoms present in the framework of substituted AFI-type materials form additional centers able to bind the benzene molecules. This is equal to an increase of heterogeneity in comparison to nonsubstituted AlPO4-5. Sorption capacity of the MeAPO-5 materials depends on both the content of metal and its distribution throughout the crystals. The distribution parameter plays an important role and may even dominate the effect of the number of metallic heterocenters. Some of the equations based on the Polanyi−Dubinin potential theory can be accepted as suitable for characterizing the distribution of the adsorption potential and adsorption energy of the AFI-type molecular sieves. The dependence between the adsorption potential and the metal content may likely be disturbed by inhomogeneous distribution of the heteroatom centers.