Zeolites transient spectroscopy

Trapped by a suitable compound, a transient intermediate can be converted into a more stable species for unequivocal identification. Stepanov and Luzgin (82) investigated the reaction of acetonitrile with 1-octene or tert-butyl alcohol on acidic zeolite HZSM-5 ( 2si/ Ai = 49) at 296 K by in situ MAS NMR spectroscopy under batch reaction conditions. Upon coadsorption of acetonitrile and 1-octene, a C MAS NMR signal at 108 ppm was observed, indicative of TV-alkylnitrilium ions 2 in Scheme 3. As depicted in Scheme 3a, the formation of these cations was explained by trapping the chemically unstable alkylcarbenium ions (formed from the adsorbed... 

Pressure Swing Adsorption (PSA) unit is a dynamic separation process. In order to create a precise model of the process and thus an accurate design, it is necessary to have a good knowledge of the mixture s adsorption behaviour. Consequently, the dilAision rates in the adsorbent particles and the mixture isotherms are extremely vital data. This article intends to present a new approach to study the adsorption behaviour of isomer mixtures on zeolites. In a combined simulation and experimental project we set out to assess the sorption properties of a series of zeolites. The simulations are based on the configurational-bias Monte Carlo technique. The sorption data are measured in a volumetric set-up coupled with an online Near Infra-Red (NIR) spectroscopy, to monitor the bulk composition. Single component isotherms of butane and iso-butane were measured to validate the equipment, and transient volumetric up-take experiments were also performed to access the adsorption kinetics. 

XPS (x-ray photoelectron spectroscopy) utilizes photoionization and energy-disperse analysis of the emitted photoelectrons to study the composition and electronic state of a region of the surface of a zeolite. However, aU these techniques are destructive ones, and for that reason other methods such as isotopic-transient experiments or reflectance [16] and fluorescence [17] imaging can be used to estimate the effective membrane thickness. 

Such FPA detector setups were first used by the group of Lauterbach for the parallel characterization of solid samples and the product gas stream from catalytic reactors [18,19]. These authors also changed the mode of operation from the previously used step-scan mode to the rapid scan mode which made it possible to even record transient processes [20,21]. The group of Lauterbach was also the first to apply FPA IR spectroscopy to a problem from zeolite science, even if it was only in form of a feasibility study. They investigated the adsorption of CO on Cu-ZSM-5 and on Pt/Si02 in order to prove that it would be possible to detect the absorption bands of adsorbed species [19J. Since experiments were carried out at room temperature, bands for CO on the Cu-ZSM-5 would be expected to have very low intensity, and indeed, no spectra for CO on this solid were shown. The band of CO on the noble metal, on the other hand, could clearly be detected without problems, and a signal-to-noise ratio not much different from that obtained for a conventional experiment. 

TRIR studies led to identification of transient Ru(PPh3)3(CO), with vCO at 1845 cm formed by reductive elimination of H2 from Ru(PPh3)3(CO)(H2). " IR spectroscopy was used to follow the adsorption of CO on Ru-exchanged NaY zeolite. Features were seen due to a linearly bound CO species and to CO adsorbed to ruthenium atoms with low coordination number. vCO bands were also used to study the effect of surface morphology on the adsorption of CO on Ru/Ti02 and RU/AI2O3 catalysts. 

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