In Y zeolites

The vanadium(IV) complex of salen in zeolite was found to be an effective catalyst for the room temperature epoxidation of cyclohexene using t-butyl hydroperoxide as oxidant.88 Well-characterized vanadyl bis-bipyridine complexes encapsulated in Y zeolite were used as oxidation catalysts.101 Ligation of manganese ions in zeolites with 1,4,7-triazacyclononanes gives rise to a binu-clear complex stabilized by the zeolites but allows oxidation with excellent selectivity (Scheme 7.4). 

Fig. 20 Cation effect on an intrazeolite singlet oxygen ene reaction in Y-zeolite.

Galletero, M.S., Garcia, H. and Bourdelande, J.L. (2003). Dramatic persistence (minutes) of the triplet excited state and efficient singlet oxygen generation for C-60 incorporated in Y zeolite and MCM-41 silicate. Chem. Phys. Lett. 370, 829-833... 

Na - K - Co exchange in Y zeolite. Heterovalent exchange reactions in zeolites generally show an even more pronounced dependency on loading (116-118). Rees (116) observed variations of the selectivity coefficient by a factor 1000 for the Na-Ca and Na-llg exchange in zeolite A at 25 °C. An+exajnple of e treipe variations is shown in fig. 9 for the K -Co and Na -Co selectivities in zeolite Y at 45 °C (117). The exchange... 

The crystal structure analysis of palladium-exchanged zeolite allows the determination of initial cation positions in the dehydrated porous framework. Similar studies after reduction by hydrogen at various temperatures should permit the observation of palladium removal from the cation sites and thus the estimation of the reduction level. Moreover, the presence of metal on the external surface is easily detected. Hence, x-ray diffraction techniques should give a good picture of hydrogen reduction of palladium in Y zeolites. 

Pd2+ tend to be the most dispersed among the eight sodalite cages, and bridged palladium ions are unlikely to occur. In conclusion, palladium ions exhibit behavior similar to that of Cu2+ (3) whereas Ni2+ ions mainly occupy SI sites in Y zeolites (7-8). 

Transalkylation reactions are observed in Y zeolites partially exchanged with ethyl-, diethyl-, and triethylammonium cations (EA, DEA, and TEA, respectively) heated above 150° C in air or under vacuum, in the presence of residual water molecules. The main reactions may be depicted schematically as follows (EA) Y — (DEA)Y > (NHt+)Y, (DEA)Y - (EA)Y > (TEA)Y, and (TEA)Y - (DEA)Y > (EA)Y, iAc main constituent in the gas phase being CJh. They are similar to those observed in montmorillonite in the presence of a water vapor pressure of a few torr. It is proposed that in both cases the transalkylation processes are acid catalyzed, the residual water molecules and the surface oxygen being the active spots recycling the protons in montmorillonite and zeolite, respectively. 

Modification of the zeolite appears to have affected the selectivity of Ru in these hydrogenation reactions. Exchange of K cations for Na cations in Y zeolite increases the basicity of the support (ref. 9). In Fischer-Tropsch reactions over similar catalysts, Ru/Y catalysts so modified yielded significant increases in the olefinic product fraction at the expense of paraffins. Olefins are believed to be primary products in F-T synthesis, with paraffins being produced from olefins in secondary hydrogenation reactions. In an analogous fashion, the Ru/KY catalyst used in the present study might also be expected to... 

Most EXAFS data show that the lattice parameter of a small particle is contracted as compared with the bulk metal. For example, Renouprez and co-workers125,135 observe for Pt encased in Y-zeolite a Pt-Pt distance contracted from 0.277 to 0.270 nm. Similarly, Hamilton et al.123 observe Cu-Cu distances varying from 0.233 for very small clusters, to 0.250 for... 

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