The isomerization and oligomerization of 1-hexene was studied over ZSM-5 catalyst under sub- and supercritical conditions within a down-flow fixed bed reactor in the temperature range of 220−250 °C and pressure range 10−70 bar. The catalyst activity and the product selectivity were found to be dependent on the operation conditions. Reactions were carried out over beds with 10 and 0.5 g catalyst, the smaller bed being used to simulate coking in the top layer of the larger bed. The conversion of 1-hexene over the 10 g bed of catalyst was in the range 83−99%, depending upon the operating conditions and was stable during the test period. An increase of the reaction temperature from 220−250 °C led to higher selectivity toward oligomerization, as did increases in reaction pressure in the range 10−70 bar. The amount of coke deposited on the catalysts decreased from 18.8 wt % at 235 °C and 10 bar in the subcritical region to 10.4 wt % at 235 °C and 40 bar in the supercritical region. DRIFTS showed that deposited coke is mainly polyolefinic. Nitrogen sorption showed that following initial shallow pore filling over shorter contact times, the pore mouth subsequently became blocked and coke mainly formed on the outside of the zeolite crystallites. When operating with 0.5 g catalyst, some deactivation occurred under subcritical conditions, although not under supercritical conditions. It appeared that with the smaller catalyst mass oligomers were retained within the pore structure of ZSM-5. The results of the study demonstrate that adjustment of the operating temperature and pressure can be used to tune the product selectivity of the reaction and the total amount of coke deposited upon the catalyst is reduced by operating under supercritical conditions.

There has been little, or no, direct testing of theories of gas sorption within particular pores situated amidst a highly inter-connected pore network. The concept of thermodynamically independent pores within networks has also been challenged. In this work, a novel integrated nitrogen sorption and mercury porosimetry technique has been used to deconvolve the condensation and evaporation processes within a specific subset of pores contained within a larger, irregular network. The sizes and geometry of these pores were obtained completely independently of gas sorption, using mercury porosimetry and NMR cryoporometry, respectively. Hence, various theories of capillary condensation, such as the Kelvin equation, the Broeckhoff-de Boer method, Saam-Cole theory, and NLDFT could be directly tested, and the potential influence of any collective network phenomena detected. It was found that, even for a shielded pore, the Cohan equation for a cylindrical meniscus gave rise to the best prediction for the relative pressure of capillary condensation, once the effects of surface chemical heterogeneity on multi-layer build-up had been taken into account. The results were also found to be incompatible with the presence of particular collective adsorption effects, such as advanced condensation.

In order to be able to make a proper interpretation of mercury porosimetry data, to obtain a structural characterization of a porous solid, a full understanding of the causes of hysteresis in mercury porosimetry is required. Several different theories have previously been proposed, but it is still difficult to make a priori predictions of the level of hysteresis anticipated. In this work, the effect of the degree of smaller scale surface roughness on the hysteresis width has been studied using mean-field density functional simulations and the results obtained confirmed by experiments on silica materials. It has been found that the hysteresis width decreases with increased degree of surface roughness, as characterized experimentally by the surface fractal dimension.

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