Sorption of gases

Sorption and desorption of gases, usually H2, have been widely used to characterize metal clusters in zeolites. [165] The methods are standard for supported metal catalysts and provide reliable measures of surface area and metal dispersion. However, when the clusters are as small as those in zeolite cages, there are important limitations to the method. For example, the stoichiometries of the reactions of H2 with metal clusters are not well known and vary from metal to metal. The method will be mentioned again in Section 4.3.3.5 for Pt dusters in the zeolite L, where the results are in good agreement with the EXAFS results. 

The measurement of the sorption of CO and of NO in combination with infrared spectroscopy gives valuable structural information about encaged dusters. Primet et al. [166] showed that the smaller the Pt duster, the higher the vibrational frequency Vnq of NO sorbed on the metal. A similar trend is expected for CO. When using this method one must be aware of the possibility that the CO or NO may cause oxidative fragmentation of the clusters or lead to cluster agglomeration. 

Other techniques expected to he of value with the appropriate metals (such as iron containing samples) are MSssbauer effect [168] and ESR [169] spectroscopies and magnetic susceptibility [170] measurements. 

CO has often been used as a convenient probe for investigating the electronic structures of metal oxide and zeolite supported metals. However, CO is not simply an innocent probe. For example, oxidative fragmentation occurs when CO reacts with Rh clusters on metal oxides or in zeolites. [171, 172] The breakup by CO of small clusters of metals that have some oxophilic character is consistent with the tendency of CO to fragment carbonyl clusters of these metals in solution. [31] 

Ouster destruction was also observed to result from NO adsorption on Pd aggregates in Y zeolite at room temperature. [174] Other examples are summarized in Ihble 4-10. 

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McBain J W 1932 Sorption by chabasite, other zeolites and permeable crystals The Sorption of Gases and Vapors by So//ds (London Routledge) pp 167-76... 

HB Hopfenberg, V Stannett. Diffusion and sorption of gases and vapors in glassy polymers. In RN Haward, ed. The Physics of Glassy Polymers. New York Wiley, 1973, pp 504-547. 

Influence of electronic impact in the rate of sorption of gases on the getter... 

McBain, J.W. (1932) The Sorption of Gases and Vapors by Solids, Rutledge and Sons, London, Chapter 5. 

It is the purpose of this article to point out the need for caution in the interpretation of many experimental results so far published in the field of catalysis and for a critical attitude toward the problem of sorption of gases, which may include adsorption on the surface as well as absorption into the interior of the structure, and may easily lead to faulty conclusions. 

This term is restricted to the sorption of gases by metals only. 

Various authors have considered the glassy state behaviour, and in particular the sorption of gases and supercritical fluids. The main dificulty is to find a thermodynamic model suitable for the description of the properties of the glassy state. Also, the normal equations of state specially developed for polymeric systems are not directly applicable to the non-equilibrium conditions of this state. 

Felder R. M., Huvard G.S. 1980, Permeation, diffusion and sorption of gases and vapors in Methods of experimental physics, 16c, 315-377, Academic Press Inc. 

Stern and his co-workers were among the first to systematically study the transport and sorption of gases and vapors in high polymers at elevated pressures. 

The concept of two or mote modes of sorption of penetrants in polymers is very familiar to cellulose and protein chemists for the case of water vapor. In fact combined Lan uir and Henry s law sorption was proposed and correctly formulated by Matthes in 1944 for water in cellulose The discovery of dual mode sorption of gases in assy polymers and the aibsequent realization that diffusion constants determined by the time lag method did not have the same ple fundamental significance a ociated whh these parameters for mbbery polymers was of profound importance. Not only were the many carefully determined diffusion coefficients in the literature of questionable value for polymers below their ass transition but a good deal of the careful peculation about solution and diffusion and the effect of... 

Many empirical equations have been proposed to describe sorption behavior of aqueous species on solid surfaces. The most conventional methods of plotting sorption data are the Freundlich and Langmuir isotherms (7). Both isotherms were developed for the sorption of gases by solid surfaces. However, they often, but not always, describe the sorption of nonelectrolytes and other species from liquid solution onto solid... 

When alternative sorbents were investigated, it was noticed that the Freundlich isotherm did not always show good congruence with the experimental data. The Dubinin-Astakov isotherm, which was originally developed for the sorption of gases, proved to be a more suitable isotherm equation for the description of the sorption process. The DA isotherm is given by... 

McBain JW (1932), The Sorption of Gases and Vapours by Solids, London, Routledge and Sons. 

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