Alkane adsorption

In situ infrared (IR) spectroscopy and calorimetry were used by the Lercher group during alkane adsorption measurements by gravimetry for various zeoHtes [5, 14]. IR spectra of the OH-streching vibrations of Bronsted acid sites in Ferrierite during adsorption of n-butane at 333°K are illustrated in Figure 13.7. 

With the model developed, we describe alkane adsorption in nanoporous crystalline and ordered acid catalysts with the intention of calculating three mathematical equations, one each for the geometry of the pore system, for describing the adsorption enthalpy and its relation with the activation energy, and for the monomolecular cracking of n-paraffins [97], This methodology can also be applied to other unimolecular reactions. 

Hydrogenolysis on a platinum metal surface proceeds through a dissociative alkane adsorption, followed by a carbon-carbon cleavage leading to methylene... 

Kinetic studies of ion exchange on partially ion-exchanged type A zeolites of Mg Ca and Mn " revealed that mini-mums and maximums characterize the differential coefficients of internal diffusion for every exchange of 2 Na " ions for one divalent cation per unit cell of the zeolite. On the basis of these observations, assuming definite interactions between the cations and the zeolite lattice, predictions can be made concerning the distribution and arrangement of cations in the unit cells of a type A zeolite. Research on liquid phase adsorption of n-alkanes on partially ion-exchanged type A zeolites indicated that the differential diffusion coefficients for alkane adsorption are influenced likewise by cation distribution in the unit cells of the zeolite. 

Qince the natural zeolites were discovered and introduced as adsorbents, numerous investigations have been devoted to the sorption behavior and ion exchange properties of zeolites 1, 2, 5, 14). Sorption behavior of zeolites can be influenced powerfully by ion exchange, partly in the uptake capacity of the zeolites and partly in sorption rate since these may undergo decisive changes. The present study undertakes, on the basis of kinetic research in ion exchange and in alkane adsorption on type A zeolites after partial ion exchange, to show what influence is exerted by cation distribution on sorption by type A zeolites. 

A. Dyer (University of Salford, Salford, Lancs., England) Were the experiments concerned with the kinetics of alkane adsorption carried out in the absence of water ... 

One main characteristics of n-butane oxidation is the substantial absence of by-products of partial oxidation other than maleic anhydride (apart from a low amount of phthalic anhydride). This means that once the alkane has been adsorbed and transformed to the first intermediate species, the latter has to be quickly transformed up to the final stable product. If this requirement is not met, the adsorbed olefinic-like intermediate may desorb. This leads to a lower selectivity to the final desired product, because the olefin may be readsorbed on nonspecific oxidizing sites yielding other undesired products (aldehydes or acids), which can also be precursors for the formation of carbon oxides. Therefore, a rapid transformation of the adsorbed intermediates to oxidized products is necessary in order to obtain high selectivity to the desired product. In order to guarantee this selective pathway, the catalyst surface must provide the required arrangement of specific oxidizing sites the different functional properties must be arranged so as to provide an ensemble of sites (or, alternatively, sites with multifunctional properties) able to allow the reaction pathway from alkane adsorption and activation up to its transformation to the final product to be completed. 

The complex iron(ll) phthalocyanine, [FePc], supported onto activated CBs [55a] by the impregnation method, was used as a heterogeneous catalyst in the oxidation of alkanes, with TBHP as an oxygen source. Carbon black proved to be an appropriate support for [FePc] complex within the framework of the oxidation of alkanes. The hydrophobicity of the support surface induced the alkane adsorption, leading to a more ideal substrate/oxidant ratio near the active center, which explained the high activity and efficiency reached with the immobilized [FePc],... 

M. Dogan, M. Alkan, Adsorption kinetics of methyl violet onto perlite , Chemosphere, 50, 517-528, (2003). 

This is a matter of some importance, as the release of adsorbed alkyl radicals to the gas phase by reaction with hydrogen is the final step in both hydrogenation and hydrogenolysis, and of course alkane adsorption initiates the latter process. A discussion of mechanism is complicated by the existence of two quite radically different proposals, which may be outlined as follows. Kemball proposed that methane is first dissociatively adsorbed as... 

Gamier, G. Glasser, W.G. Measurement of the surface free energy of amorphous cellulose by alkane adsorption a critical evaluation of inverse gas chromatography (IGC). J. Adhesion 1994, 46, 165-180. 

In work related to flotational studies Chibowski has measured the effect on the surface charge of n-alcohol and n-alkane adsorption on quartz particles from aqueous KCl solution. Maximum effect was found with Cf,—Cg n-alcohols, where the pH at the point of zero charge shifted from 5.7 to 8—9 and for Cg—C13 n-alkanes, with a corresponding shift to pH 7. 

In mesopores the sorption mass transport is less influenced by the structure and size of the alkane adsorptives than in micropores where the transport can be controlled also by geometric factors. The dynamic sorption properties of carbon nanotubes were shown to be strongly affected by the presence or absence of surface functional groups. 

In contrast to the water/alkane vapor interface, for the alkane adsorption at the aqueous solution/liquid alkane interface we have to use the adsorption equation from the liquid alkane phase as discussed in [6] ... 

Adsorption of apolar molecviles of hydrocarbons is the most sensitive to cavities size, the size of channels and various "winnows in zeolites. For example, differential heats of n.alkanes adsorption on zeolites at zero filling (obtained by extrapolation of linearly increasing section of the heat curve to zero filling) is increasing linearly with the growth of the number of carbon atoms in n.alkane molecule, and for silicalite this dependence is expressed by regression 11.6+10.0 n kJ/mol, where "u" is the number of carbon atoms in molecule. For n.alcohols adsorption heat on silicalite linear dependence is different ... 

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