Type X Zeolite with Alkaline Earth Ions

Type X Zeolite with Alkaline Earth Ions 

Silver cation (Ag+) exhibits very strong (but reversible) interactions with N2. It has been shown that LiLSX mixed with only 1-3% Ag+ can out-perform pure LiLSX in O2 production from air by PSA/VSA. Upon heat-treatment, Ag+ undergoes auto-reduction, resulting in unique cation sites that are favorable for interactions with gas molecules. The interesting properties of Ag+-containing zeolites are potentially useful for air separation as well as for other applications. Because of this, some details will be given for these zeolites. 

Chemical State and Sites of Ag In Faujasite. Silver is known to have very strong effects on the adsorption characteristics of zeolites (Habgood, 1964 Huang, 1974). Yang et al. (1996) reported the synthesis of a mixed lithium-silver (80/20) ion-exchanged X-type zeolite (Si/Al = 1.25 with 17 Ag+ per unit cell), and discussed its possible superior properties for air separation. This sorbent utilized the very strong adsorptive properties of the Ag+ ion, which 

Ab initio molecular orbital calculations showed the adsorption of nitrogen was enhanced by weak chemical interaction (through a classical n -complexation bond) with the Ag+ cation on the zeohte framework (Chen and Yang, 1996). 

It was found that, for dehydrated and fully Ag+-exchanged faujasite-type zeolites, the silver molecules were distributed among the six-ring sites (SI, SI, and Sn for faujasites) and, for samples with high A1 content, in the Sill locations. GeUens et al. (1981b) and Baker et al. (1985) showed the simultaneous occupancy of sites SI and SI by linear (Ag — Ag — Ag ) clusters. Further information (prior to 1994) can be found in a comprehensive review of silver clusters and chemistry in zeolites by Sun and Seff (1994). 

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