Tailor-made size-exclusion

Gas-solid chromatography comprises the techniques with an active solid as the stationary phase. Separation depends on differences in adsorption of the sample components on inorganic adsorbents (i.e., silica, alumina, carbon black) or on organic adsorbents such as styrene-divi-nylbenzene copolymers. Separation can also occur by a size exclusion mechanism, such as the separation of gases on synthetic zeolites or molecular sieves. GSC is performed on packed columns or on open tubular columns on the walls of which a thin layer of the porous material is deposited [porous layer open tubular (PLOT) columns], GSC nowadays is used only for special separation problems. and GSC columns are, therefore, referred to as tailor-made columns,... 

Acetate and oxygen adsorb exclusively on the bridge and three-fold Pd sites, respectively. Ethylene, however, adsorbs on Au sites where it reacts with neighboring Pd to form vinyl intermediates. These vinyl groups react with neighboring acetate to form vinyl acetate. The simulated activity and selectivity in this system was unproved by a factor of 2 and 3%, respectively. The size and shape of the Pd and Au ensembles were subsequently tailored to enhance the self assembly of ethylene and acetate imder reaction conditions and optimize the simulated activity and selectivity. The Au island sizes in Fig. 2.16, for example, were found computationally to improve the activily by an order of magnitude and the selectivity by 7%. Whether these surfaces can be made and whether or not they are stable is an important issue. Note that qualitatively very similar results were found for simulations which follow the mechanism where ethylene first couples with acetate and... 

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