The interference microscopy technique, which was recently introduced in our laboratory, is applied to study transient intracrystalline concentration profiles in ZSM-5 crystals during adsorption and desorption of isobutane. Two different zeolite samples were used, viz., samples of etched and of nonetched ZSM-5 crystals. Etching has been carried out to remove the outer layer of the crystal surface, which may contain large amounts of defects and impurities. Studying the transient concentration profiles in both samples provides unique information on the influence of surface defects on molecular uptake. It is shown that, depending on their type, the defects of the crystal surface can either increase or decrease the rate of adsorption/desorption. The former effect is associated with adsorption/desorption through cracks in the crystal surface. The latter has its origin in the blockage or structural changes of the external crystal surface, leading to the appearance of surface transport barriers. Owing to the ability of interference microscopy to gain direct insight into the influence of surface defects on molecular uptake, this technique gives more accurate information on the transport diffusivities in zeolite crystals than the classical uptake methods.

The adsorption of gases on microporous carbons is still poorly understood, partly because the structure of these carbons is not well known. Here, a model of microporous carbons based on fullerene-like fragments is used as the basis for a theoretical study of Ar adsorption on carbon. First, a simulation box was constructed, containing a plausible arrangement of carbon fragments. Next, using a new Monte Carlo simulation algorithm, two types of carbon fragments were gradually placed into the initial structure to increase its microporosity. Thirty six different microporous carbon structures were generated in this way. Using the method proposed recently by Bhattacharya and Gubbins (BG), the micropore size distributions of the obtained carbon models and the average micropore diameters were calculated. For ten chosen structures, Ar adsorption isotherms (87 K) were simulated via the hyper-parallel tempering Monte Carlo simulation method. The isotherms obtained in this way were described by widely applied methods of microporous carbon characterisation, i.e. Nguyen and Do, Horvath-Kawazoe, high-resolution α(s) plots, adsorption potential distributions and the Dubinin-Astakhov (DA) equation. From simulated isotherms described by the DA equation, the average micropore diameters were calculated using empirical relationships proposed by different authors and they were compared with those from the BG method.

Carbonaceous compounds deposited on aluminosilicate mesoporous molecular sieves of the MCM-41 type during conversion of cyclohexene at various temperatures were investigated using TGA; DRIFT, UV-vis, and 13 C solid state NMR spectroscopies; and a sorption technique. The chemical composition of the deposits is not significantly affected by the Al content of Al-MCM-41 and depends mainly on the temperature and the duration of the reaction. At lower applied temperatures, both aliphatic and aromatic compounds are formed; they are relatively weakly bound to the surface of the material. After a longer reaction period, some deposits appear that are strongly bound to the surface. At higher temperatures, a fraction of the coke migrates out of the pores. Then, part of the coke (most likely aliphatics) desorbs and moves away, while the other part (presumably aromatics) adsorbs on the external surface of the sieve. The coke remaining both in the pores and on the external surface mostly forms multilayered polyaromatic structures that are strongly bound to the surface of the material. The water sorption capacity of the studied materials decreases with the content of the deposits.

A plausible model for the structure of non-graphitizing carbon is one which consists of curved, fullerene-like fragments grouped together in a random arrangement. Although this model was proposed several years ago, there have been no attempts to calculate the properties of such a structure. Here, we determine the density, pore size distribution and adsorption properties of a model porous carbon constructed from fullerene-like elements. Using the method proposed recently by Bhattacharya and Gubbins (BG), which was tested in this study for ideal and defective carbon slits, the pore size distributions (PSDs) of the initial model and two related carbon models are calculated. The obtained PSD curves show that two structures are micro-mesoporous (with different ratio of micro/mesopores) and the third is strictly microporous. Using the grand canonical Monte Carlo (GCMC) method, adsorption isotherms of Ar (87 K) are simulated for all the structures. Finally PSD curves are calculated using the Horvath-Kawazoe, non-local density functional theory (NLDFT), Nguyen and Do, and Barrett-Joyner-Halenda (BJH) approaches, and compared with those predicted by the BG method. This is the first study in which different methods of calculation of PSDs for carbons from adsorption data can be really verified, since absolute (i.e. true) PSDs are obtained using the BG method. This is also the first study reporting the results of computer simulations of adsorption on fullerene-like carbon models.