Selective gas adsorption

Table 2. Selective gas adsorption uptakes and average particle size for both series of Pt/SBA-15 catalysts [13,16],...

Li J-R, Kuppler RJ, Zhou H-C (2009) Selective gas adsorption and separation in metal-organic frameworks. Chem Soc Rev 38(5) 1477-1504... 

Alternative techniques do exist, however, for obtaining information regarding the distribution and number of catalytic components dispersed within or on the support. Selective gas adsorption, referred to as chemisorption, can be used to measure the accessible catalytic component on the surface indirectly by noting the amount of gas adsorbed per unit weight of catalyst. The stoichiometry of the chemisorption process must be known in order to estimate the available catalytic surface area. One assumes that the catalytic surface area is proportional to the number of active sites and thus reaction rate. This technique has found use predominantly for supported metals. A gas that will selectively adsorb only onto the metal and not the support is used under predetermined conditions. Hydrogen and carbon monoxide are most commonly used as selective adsorbates for many supported metals. There are reports in the literature of instances in which gases such as NO and O2 have been used to measure catalytic areas of metal oxides however, due to difficulty in interpretation they are of limited use. 

Selective gas adsorption. The gas chromatographic technique can be cited as another example of rapid radioactive gas separation. One procedure for the separation and detection of argon, krypton and xenon activities In the coolant or exhaust gases from nuclear facilities utilizes such a method (150). 

Considerable recent efforts have been devoted to the investigation of gas separation in both rigid and porous MOF phases. Whilst only a relatively small number of systems have been investigated by selective gas adsorption measurement (as opposed to multiple measurement with various pure gases, which due to cooperative effects provides only a guide to the separation capabilities), a number of distinct separation mechanisms have been evidenced. 

Selective gas adsorption and separation in flexible MOFs is considerably more complicated than that in their rigid counterparts. Due to the high degree of cooperativity in these systems (e.g. in inducing framework deformation, the uptake of one guest can dramatically alter the uptake of another), comparison of adsorption isotherms of pure gases is of limited use and competitive measurements are essential if separation capabilities are to be determined. Due to the fact that such measurements remain very rare, and that structural information is often unavailable for the mixed-sorbed phases, only limited understandings of gas separations in flexible MOFs currently exist. 

Li JR, Tao Y, Yu Q et al (2008) Selective gas adsorption and unique structural topology of a highly stable guest-free zeolite-type MOE material with N-rich chiral open channels. Chem Eur J 14 2771-2776... 

Cheon YE, Suh MP (2009) Selective gas adsorption in a microporous metal-organic framework constructed of Co 4 clusters. Chem Commun 0 2296-2298... 

Selective gas adsorption based on size/shape exclusion... 

Figure 5 (a) Structure of MAMS-1. (b) Schematic representation of selective gas adsorption and temperature-dependent gate opening... 

Selective gas adsorption in flexible/dynamic porous MOFs... 

S. Ma, C. D. Collier and H.-C. Zhou, in Design and Construction of Metal-Organic Frameworks for Hydrogen Storage and Selective Gas Adsorption, ed. M. Hong, Wiley, Hoboken, NJ, 2009. 

Liu HK, Tsao TH, Zhang YT et al (2009) Microwave synthesis and single-crystal-to-single-crystal transformation of magnesium coordination polymers exhibiting selective gas adsorption and luminescence properties. CrystEngComm 11 1462-1468... 

The aim of this chapter is to present, in a simple and didactic way, the bases of the selective gas adsorption theory and how we can experimentally study the coadsorption of gases by using the calorimetry technique. It focuses on the energetic aspect of adsorption and on the selective physisorption of gases in microporous solids in order to use the selective adsorption for gas separation or gas purification. Thus, the thermodynamics concepts presented in this chapter are illustrated at the end by two experimental case studies on the selective adsorption in faujasite zeolites. The former is devoted to the separation of xylenes isomers, the latter to the desulphurization of natural gas. 

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